Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session T00: Poster Session III (1pm-4pm PST)Poster Undergrad Friendly
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Sponsoring Units: APS Room: Exhibit Hall (Forum Ballroom) |
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T00.00001: CONDENSED MATTER PHYSICS
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T00.00002: Observation of Fermi arcs and Weyl nodes in a non-centrosymmetric magnetic Weyl semimetal. Mazharul Islam Mondal, Anup Pradhan Sakhya, Cheng-Yi Huang, Gyanendra Dhakal, Xuejian Gao, Sabin Regmi, Baokai Wang, Wei Wen, R. -H He, Xiaohan Yao, Robert Smith, Milo X Sprague, Shunye Gao, Bahadur Singh, Hsin Lin, Suyang Xu, Fazel Tafti, Arun Bansil, Madhab Neupane Weyl semimetals (WSMs) host Weyl fermions as emergent quasiparticles resulting from the breaking of either inversion or time-reversal symmetry. Magnetic WSMs that arise from broken time-reversal symmetry provide exceptional platform to understand the interplay between magnetic order and Weyl physics, but only a few such WSMs have been realized experimentally. Here, we identify CeAlSi as a new non-centrosymmetric magnetic WSM via angle-resolved photoemission spectroscopy (ARPES) and first-principles calculations. Surface-sensitive vacuum ultraviolet ARPES data confirms the presence of surface Fermi arcs as the smoking gun evidence for the existence of the Weyl semi metallic state. We also observe bulk Weyl cones in CeAlSi using bulk-sensitive soft-X-ray ARPES measurements. In addition, Ce 4f bands are found near the Fermi level, indicating that CeAlSi is a unique platform for investigating exotic quantum phenomena resulting from the interaction of topology, magnetism, and electronic correlations. |
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T00.00003: Gapless nodal lines in a rare-earth-based semimetal Nathan A Valadez, Sabin Regmi, Robert Smith, Anup Pradhan Sakhya, Milo X Sprague, Mazharul Islam Mondal, Iftakhar Bin Elius, Andrzej Ptok, Dariusz Kaczorowski, Madhab Neupane Rare-earth-based semimetals in the ZrSiS family bring into play the potential correlation effects and magnetic ordering from the rare-earth 4f electrons in addition to the topological fermions that this family can support. Here, we investigate the electronic structure of a rare-earth-based ZrSiS-type system using the angle-resolved photoemission spectroscopy technique corroborated by density-functional theory calculations. The experimental results show the presence of multiple gapless Dirac nodes associated with multiple Dirac nodal lines in this system and these observations are well supported by calculated band structures. This work presents an insight into the topology in a rare-earth-based semimetal, which could be important to investigate its interplay with magnetic ordering, correlation effects, and spin-orbit coupling within such ZrSiS-type systems. |
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T00.00004: Longitudinal topologically protected states in a one-dimensional mechanical topological insulator. Madeleine Carhart Topological insulators are a type of material that allow the existence of unidirectional currents at the quantum scale. These currents, called edge states, are unaffected by material imperfections, which make topological insulators an active research topic with potential applications in quantum computing. Protected edge states - analogous to the unidirectional current flow of electronic topological insulators - have recently been demonstrated not only with electrons, but also with photons, sound waves, and mechanical waves [1]. Using a well-known model of topological insulators known as the Su-Schrieffer-Heeger (SSH) model [2], we constructed a one-dimensional mechanical model of topological insulators that propagates longitudinal waves in a structure of periodic vertical slabs. Using additive manufacturing, we developed a structure based on slabs with varying thicknesses to act as springs and masses. We also used a mathematical model to predict a phase transition between the insulator, conductor, and topological insulator phases of our SSH model, with clearly defined edge states in the topological insulator phase. |
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T00.00005: Magnetic order and surface state gap in Cr doped Sb2Te3 Tamal K Dalui The transition element doping in topological insulators, which breaks the time-reversal symmetry, gives |
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T00.00006: High magneto-Seebeck effect at room temperature in topological insulator Bi2-xSbxTe3-ySey crystal Pradeepta Kumar K Ghose We report thermoelectric and electrical transport properties of Bi2-xSbxTe3-ySey by tuning y for a fixed x=0.2. In contrast to the reported p-type conductivity of the end compounds with y = 0 and 3, a dominant n-type conduction mechanism is observed for y = 1.5 from the Hall measurement. Intriguingly, the magneto-Seebeck consequence is enhanced up to ∼ 20 times for y = 1.5 compared to the end members which are well known topological insulators. The reasonable value of magnetoresistance with an anisotropic character with respect to the direction of the magnetic field is observed at low temperature, which decreases with increasing temperature. The density of state at the Fermi level near room temperature correlates high Seebeck coefficient as well as magneto-Seebeck effect. High magneto-Seebeck effect at room temperature is promising for the application. |
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T00.00007: Optical conductivity of a gated Topological Insulator with a THz-transparent gate Craig S Knox, Ahmet Yagmur, Mark C Rosamond, Satoshi Sasaki, Edmund H Linfield, Alexander G Davies, Joshua R Freeman THz time-domain spectroscopy (THz-TDS) is a powerful tool to investigate topological insulator systems as the optical conductivity is sensitive to more scattering events than traditional transport measurements. As such, this technique is well suited for capturing the behaviour not just of the surface carriers, but also of the bulk carriers that dominate the transport of most topological insulator systems. However, due to the sensitivity of time-domain spectroscopy measurements, there is some ambiguity over the role the bulk and surface carriers play in the THz conductivity response. |
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T00.00008: Molecular diode overlayers for enhancing the electronic properties of topological insulators. Matthew D Rogers, Craig S Knox, Ganael Bon, Timothy Moorsom, Donald MacLaren, Mairi McCauley, Satoshi Sasaki, Bryan J Hickey, Oscar Cespedes Advancements in technology often require the coalescence of materials with a variety of properties in hybrid structures. Interface design plays a key role across many interdisciplinary fields such as thermoelectrics, photonics, and spintronics. One approach utilizes molecular films, capitalizing on the ability to design systems with specific optical, thermal, and spin physics. Similarly, topological insulators (TIs) have attracted experimental interest due to their unique band structure. Charge transport is dominated by spin-filtered edge states with suppressed scattering. These edge states represent a fascinating opportunity for research in low-loss electronics. Bismuth selenide (Bi2Se3) is one such material that is a well-developed TI system. Modifying TIs via electric field gating and doping has been shown to have a variety of applications. Increasing the bandgap (in order to inhibit bulk transport) can result in tuneable surface states and enhanced thermoelectric figure of merits. Here, we report on the growth of Bi2Se3/C60/MnPc (TI-n-p) and Bi2Se3/MnPc/C60 thin-film heterostructures grown by van der Waals epitaxy. The molecular diode junction formed between the fullerene and phthalocyanine molecule electrically gates the surface of the TI leading to large changes in the measured Hall carrier concentration and mobility. Our findings demonstrate the ability of functional molecular overlayers in tuning the electronic properties of 2-D materials for a range of applications. |
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T00.00009: Electrical and thermal hall transport in compensated topological insulator BiSbTeSe2 Rohit Sharma, Mahasweta Bagchi, Oliver Breunig, Yoichi Ando, Thomas Lorenz The existence of puddles in BiSbTeSe2 at low temperature (T <50K) has been detected using optical conductivity measurements,where DC electrical conductivity data shows an insulating behaviour,but above 50K, optical and transport results agree well with each other due to evaporation of charge puddles with increasing T[1].By comparing thermal conductivity κxx and thermal hall effect κxy data with the electrical counterparts (σxx & σxy), we study a possible influence of charge puddles on thermal transport. Electrical hall conductivity (σxy) shows hole like (p-type) behaviour at elevated T,which changes to multi-band behaviour at low T. From the electrical transport data electronic contribution to thermal transport κe was calculated by using Wiedemann-Franz law and then compared with the measured thermal transport data where it was found that both κxx and κxy shows phonon dominated behaviour. When compared κxy and κe, data matches well with each other above 50K. In contrast, below 50K κxy shows a sign change and evolves to a large thermal hall signal, whereas κe has no sign change and smoothly decreases. Possible reason for large thermal hall effect in BiSbTeSe2 will be discussed. |
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T00.00010: Phononic real Chern insulator with protected corner modes in graphynes Jiaojiao Zhu Higher-order topological insulators have attracted great research interest recently. Different from conventional topological insulators, higher-order topological insulators do not necessarily require spin-orbit coupling, which makes it possible to realize them in spinless systems. Here, we study phonons in 2D graphyne family materials. |
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T00.00011: Planar Hall effect without external magnetic field in strained Weyl semimetals Suvendu Ghosh, Debabrata Sinha, Snehasish Nandy, Arghya Taraphder The most intriguing property of a Weyl semimetal (WSM) is the chiral anomaly, i.e., the anomalous nonconservation of chiral current in the presence of external fields parallel to each other, which have been attracting intense experimental and theoretical interest. One of the fundamental manifestations of chiral anomaly in a WSM is the appearance of planar Hall effect (PHE), where an in-plane transverse voltage emerges in the presence of co-planar electric and magnetic fields. A natural quest, therefore, is whether there exists an alternate avenue to PHE, without invoking chiral anomaly. Using semiclassical Boltzmann transport theory, we show that PHE, remarkably, arises in a strained WSM even in the absence of the aforesaid anomaly and due to the strain-induced chiral gauge potential, which couples to the Weyl fermions of opposite chirality with opposite sign. Our study shows that strain causes a resultant phase shift in the current associated with opposite chirality Weyl nodes, which, interestingly, leads to a finite chirality-dependent planar Hall effect (CPHE) in the strained WSMs. We further show that a small tilt in the Weyl node can generate a pure CPHE even in the absence of an applied magnetic field. The CPHE has important implications in `chiralitytronics'. We also discuss the experimental feasibility of these novel effects in type-I strained WSMs. |
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T00.00012: Transformation of a hybridized almost-zero mode into an absolute zero mode Fargol Seifollahi, Hamidreza Ramezani For a finite-sized topologically non-trivial Su-Schrieffer-Heeger (SSH) model with an even number of sites, the existence of two almost-zero energy states which are exponentially localized on the left and right edge has been previously demonstrated. However, due to the hybridization of the modes, these states are not essentially robust against disorder; specifically in experimental setups where the system size is limited. We demonstrate that by introducing coupling defects to the initial structure, one of these topological modes is repelled from zero, whereas the other turns into an absolute zero mode localized on one of the edges of the lattice which can be robust against certain disorders in the structure. |
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T00.00013: Anomalous transport properties of Weyl semimetal CeAlSi Md S Alam, Amar Fakhredine, Mujeeb Ahmed, Pardeep K Tanwar, Hung Y Yang, Fazel Tafti, Giuseppe Cuono, Rajibul Islam, Bahadur Singh, Artem Lynnyk, Carmine Autieri, Marcin Matusiak Magnetic Weyl semimetals attract significant attention due to their nontrivial band structure and resulting unusual transport properties. Among them are the anomalous Hall and anomalous Nernst effects, which studies offer a look into details of the electronic structure. CeAlSi crystallizes in a non-centrosymmetric space group and exhibits ferromagnetic ordering below the Curie temperature (TC = 8.5 K). The Weyl points appear in its electronic structure due to broken both inversion and time reversal symmetry. We measured the anomalous Hall conductivity for two different orientations of the magnetic field (B), namely σxy for B || a and σyz for B || c, where a and c are the magnetically easy and hard axis. In the magnetic phase, σxy and σyz turn out to be of opposite sign. The sign change of the anomalous Hall effect is attributed to shifting of the Weyl point due to reconstruction of the band structure driven by spin reorientation. We also observed the anomalous contribution in the Nernst conductivity (αxy) measured for B || c. We were able to recreate the temperature dependences of σxy and αxy in the paramagnetic phase using a single band toy model assuming a non-zero Berry curvature in the vicinity of the Weyl node.Large σxy and non-vanishing αxy in the paramagnetic phase of CeAlSi appear to be consequences of the fact that the Fermi level lies close to the band crossing point. |
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T00.00014: Toward the construction of realistic model Hamiltonians for chiral spin liquids Lydia J Juan, Michael R Peterson Quantum spin liquids are an unusual phase of matter that can be formed by interacting quantum spins in certain magnetic materials and are generally characterized by their long-range quantum entanglement, fractionalized excitations, absence of ordinary magnetic order, and topological order. Chiral spin liquids are a certain type of quantum spin liquid that are known ground states for Hamiltonians with three-body spin interactions. However, Hamiltonians of this type can be considered unrealistic because the three-spin interaction does not occur as the leading term in actual magnetic systems which have Hamiltonians dominated by the Heisenberg spin-spin interaction. Determining whether a quantum spin liquid may be supported in a realistic system is important for guiding experiments toward promising platforms and materials most likely to display exotic behavior. In this work, we investigate a method, established by Peterson et al (Phys. Rev. Lett. 101, 156803 (2008)) first used for the fractional quantum Hall effect problem, to construct a realistic Hamiltonian with a topologically ordered ground state. |
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T00.00015: Dynamical probes for topological and non-Hermitian systems Paolo Molignini, Ramasubramanian Chitra, Wei Chen, Bastien Lapierre, Karin Sim, Nicolò Defenu We present several new ways of probing topological and non-Hermitian systems with dynamical tools. |
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T00.00016: Correlation between two local spins on the irradiated-doped SnTe (001) Mohsen Yarmohammadi, Michael Kolodrubetz Due to the chirality of surface states in topological materials, the optical driving of inherent spin-orbit coupling (SOC) has triggered considerable interest in condensed matter physics. Here, we study the effects of Floquet optical driving on the Ruderman-Kittel-Kasuya-Yosida (RKKY) interaction between two local spins (magnetic impurities) on the (001) surface of doped topological crystalline insulator SnTe and related alloys. Considering the region of applicability of the topological parameters in the low-energy limit, a perturbative approach employing the Floquet-Bloch states is ideal for this purpose. In contrast to the hybrid states of sublattices in the previous works with the sole role of isotropic Heisenberg RKKY term, contributing to the individual states, we find other types of interactions namely XYZ-Heisenberg, symmetric in-plane, and asymmetric Dzyaloshinskii-Moriya (DM). Generically, the RKKY Hamiltonian provides noncollinear twisted alignment for the spins. By analyzing the photo-induced isotropically band gap in the off-resonant regime, we endeavor to thoroughly show that initial ferromagnetic (FM) and antiferromagnetic (AFM) character for the spins on the same and different undoped sublattices, respectively, reaches a modulation through a circularly polarized light and dopant. We show that the novel physical insights dedicate to the chemical potential (induced by the doping agent) outside the optical gap. Although XYZ-Heisenberg and in-plane interactions oscillate, sinusoidal independent of the position of spins, the DM term oscillates approximately sinusoidal (gets a beating) for spins on the same (different) sublattices. Finally, we highlight that the intrinsic electron-hole symmetry is broken only for the DM interaction independent of the position of spins. The potential relevance to possible extensions is also briefly discussed. |
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T00.00017: Toward the construction of a realistic Hamiltonian for the bosonic Moore-Read Pfaffian state at ν=1 Carlos D Lima, Michael R Peterson Over the course of several decades physical systems that support topologically ordered phases have garnered interest due to the possibility of fractional braiding statistics among the low energy quasiparticle excitations, which hold promising practical applications. The fermionic case of the fractional quantum Hall effect at filling factor 5/2, thought to support these non-Abelian excitations, is experimentally challenging. Alternatively, the setting which can engender bosonic fractional quantum Hall states in different realistic physical systems has been established. Using exact diagonalization, we study the low-energy spectrum of a two-body model Hamiltonian generated from the three-body Hamiltonian that produces the Pfaffian as its zero-energy ground state for bosons in the spherical geometry (similar to the method used by Peterson, et al (Phys. Rev. Lett. 101, 156803 (2008)). Moreover, we analyze whether this realistic(two-body) Hamiltonian supports robust non-Abelian excitations. |
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T00.00018: Hydrogen ion implantation in lanthanum thin films for ambient pressure hydride formation Portia J Allen, Simeon J Gilbert, Michael P Siegal, Ping Lu, Peter A Sharma Near room temperature superconductivity of metal hydrides has been demonstrated experimentally at high pressures (>100 GPa). It is desirable to decrease the formation and stability pressure while retaining a superconducting hydride phase. We implanted lanthanum thin films with various doses of hydrogen ions at ambient pressure and examined the effect of superconductivity. The critical temperature decreased from 4.6 K to 3.2 K with broader superconducting transitions. Transmission electron microscopy showed increased substrate damage with increased ion dose and confirmed their granular structure. Although the superconducting hydride phase requires a higher H+ dose than measured here, we have successfully demonstrated that ion implantation at ambient pressure is a feasible technique for lanthanum hydride formation. |
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T00.00019: The fabrication of Cux(CuI)0.002Bi2Te2.7Se0.3 crystals and its superconductivity at pressures Fan-Yun Chiu, Min-Nan Ou, Yang-Yuan Chen, Ranganayakulu K Vankayala, Chih-Ming Lin We report a successful observation of pressure-induced superconductivity in the crystal Cux(CuI)0.002Bi2Te2.7Se0.3. The crystal (CuI)0.002Bi2Te2.7Se0.3was made by the so-called Bridgman method with the corresponding stoichiometric; the followed thermal treatment was employed to intercalate Cu to form Cux(CuI)0.002Bi2Te2.7Se0.3 crystals. The temperature-dependent electrical resistance was measured from 0.8 through 36 GPa. Superconductivity was detected at 3.8 GPa with Tc = 2 K. Upon further pressure increase, it reached maximum Tc = 9.3 K at 15 GPa. Over 15 GPa, the superconducting transition temperature decreased as pressure increased. Furthermore, the Hall effect measurements indicated the carrier concentration dramatically increased about five orders from ~ 1017 cm-3 at 4.2 GPa to ~ 1022 cm-3 at 15 GPa. To study the details of lattice structure migration at high pressures, the high-pressure structure investigations with synchrotron radiation were collected at various pressures from 1.97 to 44.99 GPa. Two structural phase transitions were observed at the pressures of 13.9 and 25.3 GPa, respectively at room temperature. Meanwhile, the results of pressure-dependent strain analysis on the (101) plane reveal a transition similar to the carrier concentration and superconductivity Tc at pressures lower than 13.9 GPa. This suggests that the hidden electronic phase transition may be induced by anisotropic strain in the Cux(CuI)0.002Bi2Te2.7Se0.3 in the low-pressure regime. |
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T00.00020: Coexistence Between Superconductivity and Magnetism in Dy-doped ZrTe3 single crystals Leandro Rodrigues de Faria, Lucas Eduardo Corrêa, Antonio Jefferson da Silva Machado ZrTe3 is a well-known van der Waals chain compound with a monoclinic structure [1] which bears a remarkable coexistence between superconductivity at 2.0 K and charge density waves (CDW) at 63 K [2]. Furthermore, it has been shown that its properties may be tuned by intercalation with transition metals [3], substitution with other chalcogenides [4] or defect engineering [5]. Our preliminary crystallographic through X-ray diffractometry and chemical analysis through Energy Dispersive Spectroscopy show that it is possible to obtain high quality Dy doped ZrTe3 crystals with bulk superconductivity of possible multiband nature with Tc at 5.6 K, as observed by electrical transport measurements. We also show the development of an antiferromagnetic ordering inside the superconducting state which is confirmed by means magnetization measurements, with TN at 4.3 K. |
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T00.00021: A Boson–Fermion theory that goes beyond the BCS approximations for superconductors Israel Chávez, Patricia Salas, Miguel A Solís-Atala, Manuel de Llano An analysis is given of the effects of common and recurring approximations used in conventional superconductivity theories on the condensation energy values. These approximations come from using the density of states N(ε) and the chemical potential μ(T) either constant or temperature-dependent, respectively. We use three approximations to calculate the critical temperature Tc, the superconductor energy gap Δ(T), the chemical potential μ(T) and the thermodynamic potential Ω(T) which are needed to obtain the condensation energy, and compare them with the exact case, i.e., where no approximations are used. To do this, we use a ternary Boson–Fermion theory of superconductivity composed of unbound electrons (or holes) as fermions plus two-electron and two-hole Cooper pairs, both as bosons. Although all these approximations lead to reasonable values of Tc and Δ(T), the resulting thermodynamic and chemical potentials are quite different, so that the condensation energy value could be incorrect. When N(ε) and μ(T) variables are used, together with a correct physical interpretation of the condensation energy as the sum of the thermodynamic and chemical potential differences, it leads to a better agreement with reported experimental data. |
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T00.00022: Local bistability under microwave heating for spatially mapping disordered superconductors Deepak Karki, Denis Basko, Robert Whitney We theoretically study a strongly disordered superconducting layer heated by near-field microwave radiation from a nanometric metallic tip. The microwaves heat up the quasiparticles, which cool by phonon emission and conduction away from the heated area. Due to a bistability with two stable states of the electron temperature under the tip, the heating can be tuned to induce a submicrometer-sized normal region bounded by a sharp domain wall between high- and low-temperature states. We propose this as a local probe to access different physics from existing methods, for example, to map out inhomogeneous superfluid flow in the layer. The bistability-induced domain wall can significantly improve its spatial resolution. |
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T00.00023: Simultaneous AC Susceptibility and Transport Current Study of the Intermediate Mixed State Xaver S Brems AC magnetic susceptibility is a versatile probe ideally suited to study the various states of superconducting vortex matter [1]. We have recently developed an in-situ AC susceptibility and transport measurement setup that allows for parallel neutron scattering measurements. We used this setup to study the transport and self-organization phenomena in the intermediate mixed state (IMS) in Niobium, where flux-free Meissner state domains and domains filled with vortices, called mixed state domains coexist. |
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T00.00024: Doping dependence of the critical current properties in Bi2.2Sr1.8CaCu2O8+δ single crystals Junichiro Kato, YUTARO MINO, PVAN KUMAR NAIK SUGALI, Taichiro Nishio, Shungo Nakagawa, Takanari Kashiwagi, Hiroshi Eisaki, Shigeyuki Ishida In high-Tc cuprate superconductors, the doping (p) dependence of the critical temperature (Tc) and the upper critical field (Hc2) has been intensively investigated to optimize the properties and to elucidate the electronic phase diagram. On the other hand, for the critical current density (Jc), although it is empirically known that Jc increases in the overdoped region, the detailed p dependence has not been established because Jc strongly depends on inhomogeneities such as defects and impurities. Therefore, establishing the detailed p dependence of Jc is expected to provide new insights into optimizing Jc and understanding the electronic phase diagram. |
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T00.00025: Characterization of top-gated topological insulator nanoribbon Josephson junctions grown by selective-area epitaxy Declan Burke, Anne Schmidt, Chenlu Liu, Stefanos Dimitriadis, Peter Schüffelgen, Malcolm R Connolly Topologically protected surface states in topological insulators (TIs) offer the possibility of realising topological superconductivity and hosting Majorana zero modes when proximitized by an s-wave superconductor (S). Hybrid devices with S-TI-S Josephson junctions (JJs) have been integrated into superconducting microwave circuits and provide a new platform for hybrid qubits and detecting topological superconductivity using circuit quantum electrodynamics [1]. Local gate control over the JJ carrier density would enable in-situ tuning of the Josephson energy and qubit frequency. Towards this goal we describe the fabrication and characterization of top-gated (Bi0.06Sb0.94)2Te3 TI nanoribbon JJs grown by selective-area epitaxy. |
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T00.00026: Neuromorphic Computing with Josephson Junction Neurons Leon Nichols Josephson Junctions are superconducting circuit components whose behavior can be described by a second-order, non-linear differential equation. This makes them an ideal tool for exploring and modeling complicated systems, such as neurons. This abstract will give background for studying fluxon dynamics (the behavior of a quantized amount of magnetic flux) in Josephson Junctions arrays and the possibility of demonstrating learning in a neural circuit. When cooled below TC, current loops in the array can cause fluxons to become trapped between junctions in the array. At a certain current, ISW, or thermal energy level, a fluxon will begin to move around the array, and a voltage is detectable. ISW, however, can vary significantly. It is strongly suspected that this variation is caused by production uncertainty in the size of the junctions, akin to a particle moving over hills of different sizes. Macroscopic quantum tunneling is also a suspect for these variations. The demonstration of learning involves splitting artificial neuron spikes down two different "axons" compose of more Josephson Junctions and observing the difference in arrival time of these spikes to a "learning gate" composed of an inductor and a SQUID. What we are able to observe here is called spike-timing dependent plasticity (if the spikes are close, the coupling strength is increased and vice versa). In simulations, unsupervised learning and pattern recognition have been successfully demonstrated. |
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T00.00027: Tuning the anharmonicity and frequency of multilevel system using AC Stark effect Pengtao Song, Adrian Copetudo, Clara Fontaine, Yvonne Y Gao
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T00.00028: Analysis of the Proximity Effect on Niobium Superconducting Resonators Navya Chunduru The proximity effect is a phenomenon in which superconductivity penetrates a normal, non-superconducting metal across a distance as long as the coherence length of the material. Some research has noted that the proximity effect can significantly increase the critical superconducting temperatures of superconductors. My research focuses on analyzing the interplay between two different types of thin-films (Titanium Nitride and Gold) on Niobium superconducting resonators and analyzing the serious effects that these thin-films have upon the emergence of the proximity effect and how that affects the superconducting characteristics of the resonators. I focus specifically on the superconducting and normal metal bilayers (S/N) and manipulate four different variables of magnetic field, transference, film thickness, and resonator temperature, to study the effects that such changes have on the two different types of bilayers and their overall effect on the superconducting resonators. |
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T00.00029: Discovery of a Pair Density Wave State in UTe2 Joseph Carroll UTe2 is a promising candidate material to embody bulk topological superconductivity due to spin-triplet pairing. Moreover, the newly discovered CDW state coexisting with superconductivity in UTe2 motivates the exciting prospect that a PDW state may occur. To search for a PDW in UTe2, we visualize the pairing energy-gap with μV-scale energy resolution made possible by superconductive STM tips at subkelvin temperatures. We detect three PDWs, each with gap modulations circa 10 μeV and at incommensurate wavevectors that are indistinguishable from the wavevectors of the prevenient CDW, but with a spatial-phase difference. From these observations and given UTe2 as a spin-triplet superconductor, this PDW may presage spin-triplet pair density wave physics. |
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T00.00030: Competing Incommensurate Spin Fluctuations and Magnetic Excitations in Infinite-Layer Nickelate Superconductors Christopher A Lane, Ruiqi Zhang, Bernardo Barbiellini, Robert S Markiewicz, Arun Bansil, Jianwei Sun, Jian-Xin Zhu The recently discovered infinite-layer nickelates show great promise in helping to disentangle the various cooperative mechanisms responsible for high-Tc superconductivity. However, lack of antiferromagnetic order in the pristine nickelates presents a challenge for connecting the physics of the cuprates and nickelates. Here, by using a quantum many-body Green's function-based approach to treat the electronic and magnetic structures, we unveil the presence of many two- and three-dimensional magnetic stripe instabilities that are shown to persist across the phase diagram of LaNiO2. Our analysis indicates that the magnetic properties of the infinite-layer nickelates are closer to those of the doped cuprates which hosts a fluctuating ground state rather than the undoped cuprates. The theoretically obtained magnon dispersion in LaNiO2 is found to contain an admixture of contributions from localized and itinerant carriers, in accord with corresponding RIXS experiments. Our study gives insight into the origin of inhomogeneity in the infinite-layer nickelates and their relationship with the cuprates. |
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T00.00031: Single-crystal linear conjugated polyenes through light-induced inclusion polymerization: a possible organic superconductor Steluta A Dinca Polyacetylene, (CH)n, does not dissolve in any solvent and does not melt, prohibiting formation of ordered crystals, thereby hindering its study as a potentially superconductive material. We report a new route for (CH)n chain synthesis and control over its structural order using the photochemical reaction of a reactive “guest” molecule, diiodohexatriene (DIHT), within the channels of a urea “host” crystal. Broadband light irradiation results in C-I bond scission followed by C–C bond formation and iodine (atoms or molecules) elimination from the urea structure. Continuation results in a complete loss of iodine and formation of extended, non-interacting (CH)n chains within parallel urea channels. Raman spectroscopy and mass-loss measurements are used to probe DIHT-to-(CH)n conversion and monitor iodine loss. As the urea-enclosed oligomers grow, Raman signals consistent with conjugated polyenes of known lengths are observed. With extensive irradiation, Raman signals associated with both DIHT and the growing polymer diminish, while iodine is completely expelled from the crystalline urea. These two observations indicate that polymerization goes to completion, leading to an array of isolated, fully-extended (CH)n chains within the channels. The physical properties of (CH)n in this idealized extended form, including its conductivity, may differ considerably from those of the material prepared by standard methods. The argument for high-temperature superconductivity will be discussed. |
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T00.00032: Nonmagnetic disorder effect to the FFLO phase in layered organic superconductor κ-(BEDT-TTF)2Cu(NCS)2 Shiori Sugiura, Shusaku Imajo, Motoi Kimata, Shinya Uji, Taichi Terashima, Koichi Kindo, Takahiko Sasaki Fulde-Ferrell-Larkin-Ovchinnikov (FFLO) superconductivity, which can be stabilized even above the Pauli limit, has been attracted much interest because of the exotic superconductivity beyond the framework of the BCS theory. There are two necessary conditions of the FFLO superconductivity: the quenched orbital effect and clean limit superconductivity. In the layered organic superconductors, the former condition is satisfied in magnetic fields parallel to the conducting planes. The later condition, suggesting that the FFLO superconductivity is unstable to the disorder of the electronic system, has not been systematically studied so far. |
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T00.00033: Bogoliubov-de Gennes approach to superconducting states in correlated carbon nanotubes German E Lopez, Chumin Wang In contrast to most microscopic theories of superconductivity based on the reciprocal space, the Bogoliubov-de Gennes (BdG) one provides a real-space alternative for addressing inhomogeneous systems with surface and interfaces [1]. In this work, single-walled carbon nanotubes with intertube interactions are addressed through a unitary transformation within an attractive Hubbard model [2], which decouples the self-consistent BdG equations into those of independent superconducting channels and significantly reduces the numerical solution time. The results reveal a close relationship between the local superconducting gap and the local density of states. In the limiting case of independent nanotubes, the superconducting states of carbon nanotubes can be determined by the standard Bardeen-Cooper-Schrieffer equation. Finally, the superconducting gap and critical temperature of correlated carbon nanotubes including curvature and spin-orbital effects are compared with experimental data. |
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T00.00034: Two-dimensional topological superconductivity candidate in a van der Waals layered material Jingyang You, Bo Gu, Gang Su, Yuan Ping Feng Two-dimensional (2D) topological superconductors are highly desired because they not only offer opportunities for exploring novel exotic quantum physics but also possess potential applications in quantum computation. However, there are few reports about 2D superconductors, let alone topological superconductors. Here, we find a 2D monolayer W2N3 to be a topological metal with exotic topological states at different energy levels. Owing to the Van Hove singularities, the density of states near the Fermi level are high, making the monolayer a compensate metal. Moreover, the monolayer W2N3 is unveiled to be a superconductor with the superconducting transition temperature Tc ~22 K and a superconducting gap of about 5 meV based on the anisotropic Migdal-Eliashberg formalism, arising from the strong electron-phonon coupling around the Γ point, and the 2D superconductor is phonon mediated and fits the BCS mechanism with an Ising-type pairing. Because of the strong electron and lattice coupling, the monolayer displays a non-Fermi liquid behavior in its normal states at temperatures lower than 80 K, where the specifific heat exhibits T3 behavior and the Wiedemann-Franz law is dramatically violated. Our findings not only provide a platform to study the emergent phenomena in 2D topological superconductors, but also open a door to discover more 2D high-temperature topological superconductors in van der Waals materials. |
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T00.00035: Coherent Transport vs. Realistic Phonons: Dissipation-Induced Bipolaron Localization Mattia Moroder, Martin Grundner, François Damanet, Ulrich Schollwöck, Sam Mardazad, Stuart Flannigan, Thomas Köhler, Sebastian Paeckel Recent advances in numerical methods significantly pushed forward the understanding of electrons coupled to quantized lattice vibrations. At this stage, it becomes increasingly important to also account for the effects of physically inevitable environments. In this poster, I will present a study of the Hubbard-Holstein Hamiltonian that describes a prototypical model to study the transport properties of a large class of materials characterized by strong electron-phonon coupling, in contact to a dissipative environment. Even in the one-dimensional and isolated case, simulating the quantum dynamics of such a system with high accuracy is very challenging due to the infinite-dimensionality of the phononic Hilbert spaces. The difficulties tend to become even more severe when considering an incoherent coupling of the phonon-system to an environment. For this reason, the effects of dissipation on the conductance properties of such systems have not been investigated systematically so far. In this article, we close this gap by combining the non-Markovian hierarchy of pure states method and the Markovian quantum jumps method with the newly introduced projected purified density- matrix renormalization group, creating powerful tensor network methods for dissipative quantum many-body systems. Investigating their numerical properties, we find a significant speedup up to a factor ∼ 30 compared to conventional tensor-network techniques. We apply these methods to study quenches of the Hubbard-Holstein model, aiming for an in-depth understanding of the formation, stability, and quasi-particle properties of bipolarons. Our results show that in the metallic phase, dissipation localizes the bipolarons. However, the bipolaronic binding energy remains mainly unaf- fected, even in the presence of strong dissipation, exhibiting remarkable bipolaron stability. These findings shed new light on the problem of designing real materials exhibiting phonon-mediated high-TC superconductivity. |
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T00.00036: Self-Consistent Effective Hamiltonian and its solution for the Hubbard Dimer and DImer Lattice Xindong Wang We propose a general variational fermionic many-body wavefunction that generates two quadratic chiral-symmetry broken effective Hamiltonians, each of which can then be solved exactly. |
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T00.00037: Interstitial anionic electrons in correlated transition metal compounds Tonghua Yu, Ryotaro Arita, Motoaki Hirayama Electrides are a unique family of ionic solids, which feature excess electrons confined at interstitial sites and serving as anions. The excess electrons are donated by cationic elements with a low electronegativity, standard valence, and typically a closed shell, such as alkali and alkaline earth metals. As a result, 3d-transition metals with partially filled d orbitals are not conventionally considered a suitable condition for the formation of electrides. In this work, nevertheless, we through ab-initio calculations show that magnetic 3d-transition metal compounds can also host the electride phase. We mainly focus on the oxygen-defective transition metal monoxides, MnO and NiO. With oxygen defects, the excess electrons do not transfer to the 3d orbital of Mn or Ni, but reside at oxygen vacancies and dominate the electronic structure around the Fermi level as driven by the correlation effects of 3d electrons. The resulting defective system remains Mott insulating instead of being metallic. Interestingly, a fairly high work function is obtained (3.4 eV and 3.9 eV for the defective MnO and NiO, respectively), unlike that in typical electrides (2-3 eV in general), suggesting their high chemical stability and hence a broad range of applications. Aside from defective systems, we also apply our idea to stoichiometric transition metal materials, as evidenced by M10(PO4)6 (M = Mn, Ni) and Mn3N2, which are shown to be promising electrides too. |
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T00.00038: Broadening of the Mott transition in Manganese doped Ca2RuO4 Cecilia J Abbamonte Ca2RuO4 undergoes a phase transition from a Mott insulator to a metal upon heating slightly above room temperature (357K). This transition is signatured by abrupt changes in resistivity, reflectivity, and lattice parameter lengths, which can cause extreme fracturing of samples. Small amounts of Manganese doping broaden the transition enough to mitigate fracturing during the transition while not significantly changing the temperature dependence of the resistivity. This is convenient for experiments which require larger crystals. However, even small levels of doping drastically change the temperature dependent optical properties of the material, indicating a much more gradual transition than previously thought. I present optical microscopy videos and reflectivity measurements which reveal that the metal-insulator transition is broadened more than can be deduced from resistivity measurements. I describe a percolation model which explains the shift from an abrupt transition with a long coherence length to a percolative transition when Ca2RuO4 is doped with small amounts of Manganese. In addition, the model explains the discrepancy between the abrupt change in resistivity and the gradual changes in the optical properties. |
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T00.00039: Spontaneous Excitonic Condensate in Flat Conduction and Valence Bands of Yin-Yang Kagome Lattice Gurjyot S Sethi, Feng Liu Excitonic Bose-Einstein condensation (EBEC) has drawn increasing attention recently with the emergence of 2D materials. A general criterion for EBEC, as expected in an excitonic insulator (EI) state, is to have negative exciton formation energies in a semiconductor. Here, using exact diagonalization of multi-exciton Hamiltonian modelled in a diatomic Kagome lattice, we demonstrate that the negative exciton formation energies are only a prerequisite but insu cient condition for realizing an EI. By a comparative study between the cases of both a conduction and valence flat bands (FBs) versus that of a parabolic conduction band, we further show that the presence and increased FB contribution to exciton formation provide an attractive avenue to stabilize the EBEC, as confirmed by calculations and analyses of multi-exciton energies, wave functions and reduced density matrices. Our results warrant a similar many-exciton analysis for other known/new candidates of EIs, and demonstrate the FBs of opposite parity as a unique platform for studying exciton physics, paving the way to material realization of spinor BEC and spin-superfluidity. |
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T00.00040: Tuning the antiferromagnetic ground-state of Ce2RhIn8 by Ga-substitution Gabriel Silva Freitas, Ana M Caffer, Mukkattu O Ajeesh, Maria Helena Carvalho da Costa, Samuel G Mercena, Henrique B Pizzi, Cris Adriano, Eric D Bauer, Joe D Thompson, Filip Ronning, Sean Thomas, Priscila Rosa, Pascoal Pagliuso In heavy-fermion (HF) materials, unconventional superconductivity has been found in some compounds when the long-range magnetic order is suppressed by applied pressure and/or chemical doping. In this work, we explore the effect of Ga-substitution on the physical properties of single crystals of Ce2RhIn8 through measurements of temperature-dependent specific heat, magnetic susceptibility, and electrical resistivity. Our data show a monotonic decrease of the antiferromagnetic transition temperature from TN = 2.8 K for the undoped compound to TN = 2.1 K for the highest Ga-concentration achieved (x = 0.6) in the studied Ce2RhIn8-xGax crystals. Using a mean-field model with a tetragonal crystalline electric field (CEF) Hamiltonian and isotropic nearest neighbors magnetic exchange magnetic couplings to fit our data, we have evaluated how the Ce3+ CEF scheme and exchange interactions evolve as a function of Ga-doping. Our results show that the CEF scheme presented a systematic evolution as a function of Ga-concentration with changes in the Ce3+ CEF ground state wave function. We will discuss possible scenarios and future experiments in which these compounds may show a distinct evolution to a superconducting state when compared to pure Ce2RhIn8. |
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T00.00041: Quantum Oscillations beyond the Onsager relation in a doped Mott insulator Valentin Leeb, Johannes Knolle The kinetic energy of electrons in a magnetic field is quenched resulting in a discrete set of highly degenerate Landau levels (LL). This gives rise to fascinating phenomena like quantum oscillations or the integer and fractional quantum Hall effect. The latter is a result of interactions partially lifting the degeneracy within a given LL while inter-LL interactions are usually assumed to be unimportant. Here, we study the LL spectrum of the Hatsugai-Kohmoto model, a Hubbard-like model which is exactly soluble on account of infinite range interactions. For the doped Mott insulator phase in a magnetic field we find that the degeneracy of LLs is preserved but inter-LL interactions are important leading to a non-monotonous reconstruction of the spectrum. As a result, strong interactions lead to aperiodic quantum oscillations of the metallic phase in contrast to Onsager's famous relation connecting oscillation frequencies with the Fermi surface areas at zero field. In addition, we find unconventional temperature dependencies of quantum oscillations and effective mass renormalizations. We discuss the general importance of inter-LL interactions for understanding doped Mott insulators in magnetic fields. |
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T00.00042: Nonlocal effects in 1T-TaS2 Ding Zhang, Gururaj Naik Quantum materials possess a complex energy landscape and host many interesting physical phases. As a consequence of the competition of different phases or domains, many quantum materials exhibit nonlocality and nonlinearity in optical, thermal, electrical, and magnetic responses. Light-matter interactions have been used extensively as a probe to investigate the energy landscapes of quantum materials. In this report, we study the nonlocal effect in 1T-TaS2, a charge-density-wave material at room temperature. The light tunability in 1T-TaS2 has been hypothesized to relate to the interlayer couplings and different stacking mechanisms of 2D lattices, however, the nonlocal effect rising from the domain size has not been considered in the theory of optic responses for quantum materials, creating a gap between experimental results and theory. In this study, we characterize the momentum-dependent nonlocal factor for the dielectric function of 1T-TaS2. We model the domains as 2D arrays of dipoles and generate a nonlocal susceptibility based on effective medium theory. This step would be the first approximation toward modeling and understanding the competition of phases in many other strongly correlated systems. |
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T00.00043: Magnetic excitations, phase diagram, and order-by-disorder in the extended triangular-lattice Hubbard model Johannes Knolle, Hui-Ke Jin, Josef Willsher The dynamical structure factor is an important observable of quantum magnets but due to numerical and theoretical limitations, it remains a challenge to make predictions for Hubbard-like models beyond one dimension. In this work, we study the magnetic excitations of the triangular lattice Hubbard model including next-nearest neighbour hopping. Starting from the {120deg} and stripe magnetic orders we compute the relevant magnon spectra within a self-consistent random phase approximation. In the stripe phase, we generically find accidental zero modes related to a classical degeneracy known from the corresponding $J_1$--$J_2$ Heisenberg model. We extend the order-by-disorder mechanism to Hubbard systems and show how quantum fluctuations stabilize the stripe order. In addition, the frustration-induced condensation of magnon modes allows us to map out the entire phase diagram in agreement with recent numerical works. We discuss connections to experiments on triangular lattice compounds and the relation of our results to the proposed chiral spin liquid phase. |
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T00.00044: Normal modes and anomalous viscosity of dipolar coupled BECs Camilla Polvara, Sarang Gopalakrishnan, Vadim Oganesyan We consider layered condensates interacting via contact intra-condensate interactions and dipolar inter-condensate potentials. We compute normal modes both in uniform and randomly imbalanced cases and quantify the localization in the latter using participation ratios. We also compute dipolar induced shear viscosity. |
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T00.00045: An Interaction Bulk-Boundary Relation and its Applications Towards Symmetry Breaking and Beyond Saran Vijayan, Fei Zhou Topological insulators are materials known to possess robust boundary states whose low energy excitations resemble that of half the massless Dirac fermions, with the other half being localized at the opposite boundary. Hence, an attractively interacting topological surface naturally results in a topological superconducting phase (TSC) that hosts emergent |
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T00.00046: Stable magic angle and van Hove singularity in twisted bilayer Graphene with proximitized spin orbit coupling Cheng Xu, Yang Zhang, Yong Xu, Wenhui Duan We propose that the electronic structure of magic-angle twisted bilayer graphene can be stabilized by the proximitized Kane-Mele spin-orbit coupling. These terms bring a quadratic dispersion relation between the bandwidth and twisted angle, which leads to stable van Hove singularities even with angle disorders. We then investigate the fractional Chern insulator(FCI) as an example, and find the FCI indicator gets significantly reduced with the Kane-Mele spin-orbit coupling. Furthermore, in hBN encapsulated twisted bilayer Pt$_2$HgSe$_3$ with intrinsic Kane-Mele spin-orbit coupling, we identify a topological flat band at a large twist angle($>4 ^circ$). |
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T00.00047: Nonequilibrium thermoelectrics of a Kondo-correlated molecular junction Anand Manaparambil, Ireneusz Weymann Thermoelectric properties of nanostructures, such as quantum dots or molecular junctions, have been shown to contain the signatures of the Kondo correlations. Such systems have been extensively investigated theoretically in the equilibrium regime, whereas the nonequilibrium thermoelectric behavior has been much less explored due to difficulties arising when treating electron correlations accurately at out-of-equilibrium conditions. Here, we study the nonequilibrium thermoelectrics of a molecular junction with asymmetric coupling to the leads. This asymmetric coupling, present in various experimental setups, allows for treating the weakly coupled subsystem perturbatively whereas the strongly coupled part is accurately solved by using the numerical renormalization group method. We demonstrate that the electron transport across such a junction with finite potential and temperature gradient can be calculated using perturbation theory and it contains the signatures of the Kondo correlations. Furthermore, we study the behavior of the Seebeck coefficient, extended to the non-equilibrium regime, for different system parameters, and observe new regions of sign change in the non-equilibrium Seebeck coefficient due to the presence of Kondo correlations. |
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T00.00048: Numerical renormalization group study of Loschmidt echo in Kondo system Kacper Wrzesniewski, Tomasz Slusarski, Ireneusz Weymann
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T00.00049: A candidate of a ferromagnetic quantum critical point: an investigation of the Ni1-xCux alloy Rong-Zhu Lin, Wei-Tin Chen, Chien-Lung Huang In metallic magnetic systems, a second-order phase transition temperature could be tuned to absolute zero by introducing non-thermal tuning parameters, reaching a quantum phase transition where the quantum fluctuations destroy the magnetic order and dominate physical properties therein. In this report, we take an investigation into an itinerant ferromagnetic system, Ni1-xCux alloy. From isothermal magnetization data, we performed an Arrott-Noakes analysis to determine the transition temperature TC and found TC→0 in Ni1-xCux with x = 0.66. Strongly chemical disorder is induced as Cu is alloyed with Ni evidenced by a negative temperature coefficient of electrical resistivity, i.e., the resistivity increases slowly as the temperature decreases. The electronic contribution to the specific heat shows divergent behavior as the temperature decreases. These results may indicate an existence of the ferromagnetic quantum critical point in Ni1-xCux, tuned by chemical disorder. |
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T00.00050: Numerical Study of the Doped 1/5-Depleted Square Lattice Hubbard Model Ehsan Khatami, Brendan Stork, Eduardo Ibarra Garcia Padilla, Richard T Scalettar We study magnetic properties of the doped Fermi-Hubbard model on the 1/5-depleted square lattice using exact diagonalization of small clusters and the density matrix renormalization group. The model at half filling has been shown to exhibit multiple phase transitions as the ratio of hopping amplitudes on the two distinct bonds of the lattice changes. Here, we focus on the model away from half filling and map out its rich magnetic phase diagram as the density, interaction strength and hopping ratio change. We discuss the potential for the simulation of the model using programmable tweezer array of fermions. |
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T00.00051: Bulk-boundary correspondence for intrinsically-gapless SPTs from group cohomology Rui Wen, Andrew C Potter
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T00.00052: Hydrodynamics with helical symmetry Jack Farrell We present the hydrodynamics of fluids in three spatial dimensions with helical symmetry, wherein |
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T00.00053: A MaxEnt-μSR study: Short-range ordering above the Verwey transition of Fe3O4 Carolus Boekema, Carlos A Morante Using muon-spin rotation (μSR) the magnetic fields of Fe3O4 have been previously investigated. [1] The Verwey transition at Tv (~123 K) and a transition at Tw (~247 K) are observed. Using the sensitive Maximum-Entropy (MaxEnt) method, single-crystal-Fe3O4 μSR data are analyzed. [2,3] We review earlier results [3] and report the T-dependence of fields with Bext (720 Oe) // <110>. Below the demagnetization field, extra μSR signals are found at Bext // <110> indicating two frequencies at room temperature (RT) and two at 205 K. [3] At RT, the upper frequency follows the zero-field (ZF) trend seen in the Tv-Tw region of the ZF phase diagram. At 205 K, the lower frequency follows the extension of the ZF trend above Tw. These two ZF trends indicate short-range ordering related to electron conduction behavior and to precursor effects of the Tv transition. [1] Our MaxEnt-μSR finding is consistent with diffuse [4] & x-ray [5] scattering results above Tv. This interpretation shows two magnetizations, reflecting different short-range orders [3-5] in the ZF Mott-Wigner Fe3O4glass phase. |
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T00.00054: Evidence for orbital correlations and incipient orbital magnetism in ultrathin Co/Ni films Joshua Peacock, Sergei Ivanov, Sergei Urazhdin We present experimental evidence for orbital magnetism in heterostructures including ultrathin (111)-oriented Co/Ni bilayers. Magnetoelectronic measurements based on the anomalous Hall effect (AHE) show a nonlinear feature which appears on the background of paramagnetic response above the Curie point Tc of ferromagnetic films. The dependence on the magnetic field and temperature associated with this feature is well-described by the Landau theory of phase transition, with the transition temperature above Tc. The amplitude of the feature is maximized for equal thicknesses of Co and Ni. |
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T00.00055: Optically Active Graphenic Nanoflakes: the h-BCN Monolayers Joel Turallo, Wai-Ning Mei, Renat Sabirianov, Lu Wang, Lauren E Samson, Peter A Dowben, Carolina C Ilie Hexagonal-BCN has shown to be a practical and useful alternative to graphene monolayers for many applications including many electronic devices and photochemical processes. Hexagonal BCN (h-BCN) has a larger band gap and desired semiconducting properties. While h-BCN is isoelectronic to graphene, it is chiral and it has the advantage of being optically active near VUV, at wavelengths much higher than graphene nanoflakes. The first principles Density Functional Theory calculations are used to explore the band structure profile of h-BCN. Hydrogen terminated h-BCN nanoflakes are planar and its stability confirmed by calculations. The absorption energies of h-BCN on Rh(111) as well as the other face-centered cubic metals like Ir(111) and Ni(111) are calculated. Surprisingly, nanoflakes of h-BCN do not always lay flat on the surfaces of all metals but appear to adopt a corrugated orientation. |
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T00.00056: Surface roughness noise and comprehensive depth-dependent noise effects on coherence time of NV centers in diamond Philip C Chrostoski, Pauli Kehayias, Deborah H Santamore Noise is a detrimental issue for nitrogen-vacancy (NV) centers in diamond, causing line broadening and decreasing the coherence time (T2). We investigate noise caused by the diamond surface roughness, which is a source for charge density fluctuations and incoherent photon scattering. We find that the varying surface charge density noise source is prevalent throughout the entire NV dynamical decoupling frequency range, while the photon scattering noise is almost negligible. Next, we perform comprehensive analyses on T2 and how it varies with NV depth. At a depth of 5 nm below a hydrogen- or fluorine-terminated surface, these magnetic nuclei reduce the NV coherence time the most, followed by the surface electric field noise sources. The photon scattering, bulk magnetic field noise, and oxygen surface termination effects on T2 are weak compared to the varying charge density, electric dipole, and surface impurity noise. Our calculated values of T2,Hahn (μs range) are in good agreement with the experimental values reported elsewhere. Finally, we calculate an anticipated signal-to-noise ratio (SNR) for NV AC magnetometry of external nuclear spins. In our simplified assessment (e.g. some depth dependent parameters are held constant), we find that shallower NV layers should yield the best SNR, which is consistent with experimental findings. |
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T00.00057: Quantum Buckling in Metal–Organic Framework Materials R. Matthias Geilhufe Metal–organic frameworks are porous materials composed of metal ions or clusters coordinated by organic molecules. As a response to applied uniaxial pressure, molecules with a straight shape in the framework start to buckle. At sufficiently low temperatures, this buckling has a quantum nature described by a superposition of degenerate buckling states. Buckling states of adjacent molecules couple in a transverse field Ising type behavior. Based on the example of the metal organic framework topology MOF-5, we derived the phase diagram under applied strain, showing a normal phase, a parabuckling phase, and a ferrobuckling phase. At zero temperature, quantum phase transitions between the three phases can be induced by strain. This novel type of order opens a new path toward strain induced quantum phases. |
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T00.00058: Ohmic carrier transport at the edge-contacted 2D MoS2 field effect transistors Sungwon Lee, Hoseong Shin, Won Jong Yoo Vertically stacked transistors using two-dimensional (2D) materials are emerging, for which a technique to precisely etch the vertically stacked 2D layered structures needs to be developed. In particular, the development of edge-contacted devices fabricated by plasma etching of the stacked structure where a metal is deposited is very important. When a metal and a 2D semiconducting material are brought into contact, Schottky barrier is formed at the interface, resulting in suppression of electronic carrier transport. However, when the metal is brought into contact with the edge of the 2D semiconducting material, an improvement in carrier transport can be expected due to the absence of the Schottky barrier. In this research, we fabricate edge-contacted field effect transistors (FETs) by bringing metal into contact with the edge of 2D molybdenum disulfide (MoS2). We find that these FET devices exhibit Schottky contact behavior in the temperature range of 73 to 413 K but exhibit ohmic contact behavior in higher temperatures (above 433 K). Also, the ohmic behavior is observed depending on the metals used; ohmic contact is realized when metals having a high work function (palladium or gold) or semi-metals (bismuth or antimony) are brought into contact with MoS2. |
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T00.00059: Probing the Functionalized Black Phosphorus Surface through Advanced Microscopy Michael Riehs, Kendahl L Walz Mitra, Kevin Ho, David Ginger, Alexandra Velian Surface functionalization of two-dimensional materials by solution phase methods is a key step towards scalable tuning of their physical and chemical properties, yet experimental strategies to directly probe and image the resulting modified surfaces are scarce. Semiconducting few layer black phosphorus (bP) is of particular interest among two dimensional materials due to its thickness dependent bandgap and highly reactive surface making it amenable for functionalization. We have shown in past work that the surface of bP can be functionalized with discrete molecular fragments, such as organic groups and Lewis acids, altering its physical and electronic properties. While bulk measurements, such as vibrational spectroscopy and X-ray photoelectron spectroscopy (XPS), report on success of functionalization and structure of the functional group on bP, the exact location and surface density of these fragments have yet to be determined. Herein, we introduce a facile solution phase protocol to modify the surface of bP with discrete organometallic fragments and directly image them using photoinduced force microscopy (PiFM) and electron microscopy methods. PiFM is used to track organometallic fragments by measuring site specific vibrational frequencies on bP flakes. This not only provides a map of the fragments on each flake, but also reveals information on the local binding environment surrounding the metal atom. Along with this scanning probe method, high resolution transmission electron microscopy (HRTEM) and scanning transmission electron microscopy (STEM) coupled with annular dark field (ADF) and energy dispersive X-ray spectroscopy (EDS) detection is employed to image the organometallic fragments attached to the bP surface revealing both single metal atom sites and small metallic clusters along the basal plane and edges. This solution phase protocol and imaging characterization opens a new dimension to tune the bP surface and therefore its electronic properties. |
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T00.00060: Real Space Observation of Structural Phase Segregation in Fe5GeTe2 using STM/STS Barnaby R Smith Fe5-xGeTe3 is a material that exhibits highly sought-after properties, having a Van der Waals coupled 2d structure and exhibiting itinerant ferromagnetism down to the monolayer limit with a near room temperature Tc.1 These make it a useful tool to add to the device physicists toolbox of materials to make heterostructure devices with. A remaining problem that hinders our total understanding of the material however is its complex crystal structure, with inherently split sites combined with a strong tendency to be Fe deficient leading to differing phases with locally broken inversion symmetry.2 A fuller picture of the microstructure of these phases and their electronic structures is therefore desired to clarify these issues. |
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T00.00061: Valley spin acoustic resonance in monolayer MoS2 Kabyashree Sonowal, D.V Boev, A.V Kalameitsev, Vadim Kovalev, Ivan Savenko Monolayer molybdenum disulphide (MoS_2) is a strong candidate material to study spin-valley coupled physics in 2D materials. Its unique band structure consists of spin-split subbands crossing each other at finite momenta with opposite spin orientation in both the valleys. When exposed to Rayleigh surface acoustic waves, strain-induced pseudomagnetic fields couple with spin resulting in spin-phonon interaction. We theoretically predict the occurrence of spin acoustic resonance accompanied by an acoustoelectric current due to spin-flip transitions between the spin-split subbands. We calculate the transition probabilities, obtain the conditions for observing spin acoustic resonance and calculate and study the behaviour of the acoustoelectric current. On breaking time reversal symmetry, both the spin acoustic resonance and acoustoelectric current become valley sensitive paving the way for acousto-electric spectroscopy of valley selective phenomena. |
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T00.00062: Broken Symmetry and Charge Transfer in InSe-GaSe Heterostructures Greyson B Voigt Van der Waals heterostructures allow for stacked 2D materials to impart properties to each other, often through charge-transfer effects or via breaking various symmetries. InSe itself has notable Rashba Spin-orbit coupling in a inversion-symmetry breaking electric field. Here, we fabricate an InSe-GaSe heterostructure in order to further break the inversion symmetry of the InSe, aiming to enhance the spin-orbit coupling, and to examine charge transfer effects in the sample. |
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T00.00063: Plasmon-exciton interaction in gold nanotriangle covered MoSe2 monolayers Samia Alyami, Matthew Larson, Hans Peter Wagner, Yang Pan, Lu He, Dietrich RT Zahn, Heidrun Schmitzer We investigate the interaction between plasmons and excitons in gold nanostructure decorated MoSe2 layers. The monolayers are mechanically exfoliated and transferred using an all-dry viscoelastic stamping technique onto a sapphire substrate. The photoluminescence of bare single and bilayer MoSe2 samples at room temperature revealed exciton emission at 786 nm in the single layer and 807 nm in the bilayer. The PL intensity of the bilayer is quenched by an order of magnitude due to its indirect bandgap. The monolayers are covered with a gold nanotriangle (NT) array using nanosphere lithography with polystyrene beads. The shape and the height of the gold NTs were determined with Atomic Force Microscopy (AFM) and Scanning Electron Microscopy (SEM). The plasmon resonance of the gold NT arrays was investigated with transmission measurements and compared with COMSOL simulations as a function of gold triangle height and polystyrene diameter. Coupling between the gold NT plasmon resonance and the exciton emission of the MoSe2 monolayer is examined using photoluminescence and transmission measurements. |
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T00.00064: Electric field tunable hybridization in MoSe2 bilayers Xiaohui Liu, Zhida Liu, Yue Ni, Di Huang, Jiamin Quan, Hyunsue Kim, Yanxing Li, danfu liang, Frank Y Gao, Yongxin Zeng, Nemin Wei, Takashi Taniguchi, Kenji Watanabe, Chih-Kang Shih, Allan H MacDonald, Xiaoqin Elaine Li
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T00.00065: Plasmonic gain in current biased tilted Dirac nodes Sang Hyun Park, Michael J Sammon, Eugene J Mele, Tony Low Surface plasmons, which allow extreme confinement of light, suffer from high intrinsic electronic losses. It has been shown that stimulated emission from excited electrons can transfer energy to plasmons and compensate for the high intrinsic losses. To-date, these realizations have relied on introducing an external gain media coupled to the surface plasmon. Here, we propose that plasmons in two-dimensional materials with closely located electron and hole Fermi pockets can be amplified, when an electrical current bias is applied along the displaced electron-hole pockets, without the need for an external gain media. As a prototypical example, we consider WTe2 from the family of 1T′-MX2 materials, whose electronic structure can be described within a type-II tilted massive Dirac model. We find that the nonlocal plasmonic response experiences prominent gain for experimentally accessible currents on the order of mA µm−1 . Furthermore, the group velocity of the plasmon found from the isofrequency curves imply that the amplified plasmons are highly collimated along a direction perpendicular to the Dirac node tilt when the electrical current is applied along it. |
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T00.00066: Using polarized twisted light to tailor the superposition of finite-momentum valley exciton states in transition-metal dichalcogenide monolayers Guan Hao Peng, Oscar J Gomez Sanchez, Wei Hua Li, Ping Yuan Lo, Shun Jen Cheng A twisted light is a spatially structured light that carries a new degree of freedom of quantized orbital angular momenta (OAM), which, in addition to that of intrinsic spin angular momentum (SAM), i.e., polarization, is appealing for new quantum information technology. In this talk, we will present a theoretical study of the photo-excitation of valley excitons in transition-metal dichalcogenide monolayers (TMD-ML's) by using polarized Laguerre-Gaussian beams, one of the best-known twisted light's (TL's). Our studies show that the photoexcitation of polarized TL incident to a TMD-ML leads to the formation of the superposition of finite-momentum exciton (SFME) states, forming an exciton wave packet whose geometric pattern over the momentum and real spaces are encoded by the optical OAM. Furthermore, the momentum-dependent optical matrix element (MD-OME) of the SFME states for the exchange-split longitudinal and transverse exciton bands of TMD-ML's under TL excitation are shown to be highly directional and dependent on the polarization of the applied TL. The MD-OME's of the SFME states under the linearly polarized TL excitation mimic an exciton multiplexer allowing for selectively detecting the optical signatures of the meV-split longitudinal and transverse exciton bands of TMD-ML's. |
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T00.00067: Chiral nanophotonic interfaces for near-field optical control of two-dimensional semiconductors Robert T Shreiner, Kai Hao, Andrew H Kindseth, Alexander A High The evanescent fields of waveguided optical modes in nanophotonic structures exhibit transverse spin angular momentum. These circularly polarized fields, which depend on position and propagation direction, enable reconfigurable interactions with circularly dichroic materials. Monolayer transition metal dichalcogenides (TMDCs) host valley-selective, circularly polarized optical transitions. Moreover, due to spin-valley locking in monolayer TMDCs, the spin degree of freedom of charge carriers can be manipulated. Here, we fabricate titanium dioxide (TiO2) nanophotonic structures on gated, encapsulated tungsten diselenide (WSe2) monolayers. We demonstrate near-field optical control of the spin polarization of resident electrons, illustrating the potential use of such interfaces for integrated photonics and opto-spintronics. |
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T00.00068: Theoretical modelling on new level crossings and electron-hole asymmetry in Landau octet of bilayer graphene Abhay Gupta, Feixiang Xiang, Andrey Chaves, Kenji Watanabe, Takashi Taniguchi, David Neilson, Francois M Peeters, Milorad V Milosevic, Alexander R Hamilton The highly tunable band structure and eightfold degeneracy of the zero-energy Landau level (zLL) of bilayer graphene (BLG) make it an ideal platform for engineering new quantum Hall states, denoted by the orbital, valley, and spin quantum numbers. However, determining the orbital, valley, and spin order of quantum Hall states at different filling factors and electric fields is still an unresolved question. In the experiments, we observe new zero-energy Landau level crossings at filling factor -2, 1 and 3 in high electric fields at millikelvin temperatures. These observations enable us to constrain the parameters for constructing a simplified effective single-particle theoretical model, which can be used to fully determine the quantum Hall states. The model predicts the importance of coulomb interactions in this system via exchange-enhanced Zeeman g-factor. |
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T00.00069: Mechanically reconfigurable electron confinement in vdW heterostructures via sliding gates yuhui yang, Andrew Barabas, Ian Sequeira, Aaron H Barajas Aguilar, Takashi Taniguchi, Kenji Watanabe, Javier D Sanchez-Yamagishi Van der Waals (vdW) heterostructures are very sensitive to their layer structure and orientation, and the low friction between layers allows devices to be reconfigured to modify layer orientation and overlap, which strongly affects their physical properties. We have discovered that microscale gold features deposited on vdW materials can also slide with very low friction. Deposited gold allows for near arbitrary patterning, enabling electrical contact and a strong mechanical grip to move smaller vdW flakes. This greatly expands the scope of possible vdW heterostructure manipulation experiments. |
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T00.00070: THz Phonon Generation in Graphene Driven Out of Equilibrium Jasen Zion, Aaron H Barajas Aguilar, Ian Sequeira, Andrew Barabas, Kenji Watanabe, Takashi Taniguchi, Javier D Sanchez-Yamagishi In ultraclean graphene devices driven out of equilibrium, electrons can reach high drift velocities with relative ease. When the drift velocity of electrons exceeds the speed of sound in a material, stimulated phonon emission dominates over absorption. This can result in an amplification of THz frequency phonons in the direction of carrier flow. We explore the local electrical properties along long graphene devices, observing a 7-fold increase in resistivity over a distance of 8 microns. Phonon amplification is demonstrated under a wide range of carrier densities (0.5 to 4*10^12 cm^-2) and temperatures (1.5 to 280K). The resulting inhomogeneous resistivity could modify electron transport measurements in similar devices and act as another effect for consideration for long graphene devices. Our findings suggest future applications as a novel on-chip THz phonon generator, which could be coupled to other 2D materials to modify crystal structure on the order of the atomic lattice. |
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T00.00071: Absorption spectra of graphene nanoribbons in external electric and magnetic fields Po-Hsin Shih, Thi-Nga Do, Godfrey Gumbs, Danhong Huang We investigated the electronic and optical properties of nanoribbons (GNRs) subject to in-plane transverse electric and perpendicular magnetic fields. The numerical calculations were carried out within the generalized multiorbital tight-binding model based on a Hamiltonian which takes into account hopping integrals among the (s,px,py, and pz) atomic orbitals. The band structure consists of π bands arising from the pz orbital and σ bands originating from the (s,px, and py) orbitals. We found that the energy bands and optical spectra of GNRs can be manipulated efficiently by the edge configuration, armchair or zigzag, and the strength of the external fields. The optical absorption spectra are enriched by exotic characteristics of band structure such as band gap, flat bands, band splitting, shifted of Fermi level, and magnetic quantization. With the rich and unique properties, GNRs are suitable candidates for applications in the fields of photodetectors, nanoelectronics, and spintronics. Our theoretical prediction could be verified by angle-resolved photoemission spectroscopies and optical spectroscopies. |
Author not Attending |
T00.00072: Optical absorption of gate-controlled twisted bilayer graphene at infrared frequencies Eunjip Choi, KwangNam Yu, Pilkyung Moon We report an infrared transmission measurement on electrically gated twisted bilayer graphene. The optical absorption spectrum clearly manifests dramatic changes such as the splitting of the interlinear-band absorption step, the shift of the inter-van Hove singularity transition peak, and the emergence of a very strong intravalence (intraconduction) band transition. These anomalous optical behaviors demonstrate consistently that electron band of the TBG undergoes a nonrigid modification against the Fermi level shift by ion-gel gating. We compare it with theoretical band calculation in which an electronic screening and layer-asymmetry are explicitely taken into account. We propose that this band modification may be universal to other twsisted 2d material. |
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T00.00073: The interplay of field-tunable strongly correlated states in Γ and K moiré bands in a heterotrilayer device Aidan J Campbell, Valerio Vitale, Mauro Brotons-Gisbert, Hyeonjun Baek, Kenji Watanabe, Takashi Taniguchi, Jonathan Ruhman, Johannes C Lischner, Brian D Gerardot In twisted transition metal dichalcogenide (TMD) heterobilayer systems the moiré bands that form the highest valence band generally arise from K-derived states. However, as more layers are added for naturally stacked TMDs the Γ valley becomes energetically relevant. Here, we optically probe the exciton-polarons in the presence of correlated states in a heterotrilayer 2H-bilayer WSe2/monolayer MoSe2 moiré heterostructure. We observe the formation of exciton-polarons where the direct exciton at ±K is dressed by holes residing in Γ derived moiré bands, evidenced by their distinctive hole-doping dependent dispersions. As the number of holes per moiré unit cell is tuned, abrupt changes of the attractive polarons reveal the formation of strongly correlated hole states within the Γ bands at both integer and intermediate fractional fillings. Upon application of a vertical electric field we change the ordering of Γ- and K-derived bands and transfer holes between Γ and K correlated states. Further, the WSe2 attractive polarons dressed by the Γ and K correlated holes reveal contrasting polarisation properties under an applied magnetic field. The results are fully supported by density functional theory calculations which show highest Γ band projects onto a honeycomb lattice with inequivalent A and B sites, while the K band forms a triangular lattice. Our results reveal the potential of heterotrilayer TMDs for Hubbard model investigations for both honeycomb and triangular lattices within the same devices. |
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T00.00074: Moiré-Trapped Interlayer Exciton dynamics in a WSe2/MoSe2 Heterobilayer Shun Feng, Aidan J Campbell, Mauro Brotons-Gisbert, Hyeonjun Baek, Kenji Watanabe, Takashi Taniguchi, Brian D Gerardot Transition-metal dichalcogenide heterobilayers can host interlayer excitons (IXs) trapped in moiré potentials with tailored electronic band structures and strong dipolar interactions, promising for realizing exciton ordering and nonlinear exciton switches at quantum limit. The temporal dynamics of moiré-trapped IXs can offer extra insight into how the IXs are interacting in the moiré trapping site, yet it is thoroughly studied. Here we use CW photoluminescence (PL) spectroscopy to reveal the evolution from single photon emitters to broad spin singlet/triplet ensemble peaks of moiré-trapped IX in a charge neutral WSe2/MoSe2 heterostructure, highlighting a dipolar-induced Coulomb interaction which results in up to 8.5 meV blue shift in emission energy. Complementary to the spectral feature, using pulsed laser excitation we reveal the power-dependent lifetime of the spin triplet exciton ensemble peak. As we increase power across three orders of magnitude, we observe a continuously decreasing lifetime. We interpret the evolution of the temporal dynamics by considering strong dipolar interactions, exciton density (i.e., inter-exciton distance) as well as the exciton-exciton annihilation rate. Our study provides insights for exciton dynamics in state-of-the-art moiré heterobilayers, and represents a steppingstone to pursue complex phenomena like quantum phase transitions of IXs. |
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T00.00075: Robust, gapped, flat bands at half-filling in the minimal model of the superconducting metal-organic framework, Cu-BHT Henry L Nourse, Miriam F Ohlrich, Ben J Powell Flat band systems and strong electronic correlations promise to be a playground for unconventional phases of matter, such as high-temperature superconductivity and other strongly correlated phenomena. Understanding superconductivity in strongly correlated electron systems is one of the grand challenges of modern physics. There has recently been large interest in flat bands with the discovery of superconductivity in twisted bilayer graphene but designing materials with flat bands is difficult. |
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T00.00076: Optical Characterization of Tensile Strained Germanium and Gallium Arsenide Quantum Dots Joseph W Spinuzzi, Michael Scheibner, Christopher F Schuck, Kathryn E Sautter, Paul J Simmonds, Christian Ratsch Strain as an additional knob in quantum dot growth offers the ability to tailor a material for sensors or quantum applications like quantum communication in the standard telecommunication bands. Here we are investigating tensile strain germanium and gallium arsenide quantum dots for tuning their optical transitions into and across the mid infrared spectral region, gathering correlations between strain and confinement that define the quantum dots’ optoelectronic properties. With strain many semiconductors’ properties can be tailored. Indirect bandgap materials like germanium can be tuned into direct bandgap materials. With photoluminescence and Fourier-transform infrared spectroscopy we determine the nature of these quantum dots, illuminating band gap characteristics, emission efficiencies, and other optoelectronic properties. Preliminary results indicate a direct emission from the strained quantum dots. Using resonate Raman spectroscopy the percent strain a quantum dot undergoes from the host material is measured. The interplay between strain and confinement through their effects on optical response is mapped and an overall correlation is derived. |
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T00.00077: Plasmons in Atomically Thin Crystalline Silver Nanostructures Grown on Patterned Silicon Andrew P Weber, Vahagn Mkhitaryan, Laura Fernández, Zakaria M Abd El-Fattah, Ignacio Piquero-Zulaica, Kevin Garcia Diez, Frederik M Schiller, Jose E Ortega, Javier Garcia de Abajo We demonstrate the fabrication of ultrathin, crystalline Ag nanostructures on pre-patterned Si substrates and characterize their novel plasmonic properties. Nanostructures are first produced by etching the Si(111) substrate by electron beam lithography. This is followed by wet chemical etching to remove resist and native Si-oxide from the surface, which is then coated with ultrathin (less than 5 nm), crystalline Ag by molecular beam epitaxy. The preparation steps are monitored by electron spectroscopy and microscopy methods. High quality mid-infrared plasmonic resonances of the resulting nanostructured Ag are characterized by Fourier transform infrared spectroscopy. Multiple higher-order modes are found in various types of nanostructures (e.g. triangles, bowties, disks). Our process results in Ag nanostructures covered with only a thin passivating layer, which is advantageous for interfacing and chemical sensing applications. |
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T00.00078: GaAs-based superlattice photocathodes manufactured using MOCVD provide spin polarization > 90% and quantum efficiency > 1% Matt Poelker Spin-polarized electron beams are important for nuclear physics research performed at electron accelerators. Over many years, beam polarization has increased significantly, from 35% provided by unstrained bulk GaAs, to ~ 75% using single strained-layer GaAs, to ~ 90% using strained-superlattice GaAs photocathodes grown using molecular beam epitaxy (MBE). Commercial vendors once provided high-polarization photocathodes but today there is little interest in supporting this small market. Here, we report successful results fabricating high polarization GaAs/GaAsP superlattice photocathodes using metal organic chemical vapor deposition (MOCVD), a method dismissed by some as not providing sufficient control of layer thickness and uniformity. The best samples provide spin polarization greater than 90% and quantum efficiency exceeding 2%, with quantum efficiency enhanced using a distributed Bragg reflector incorporated into the structure. Together, these quantities represent some of the best results ever reported for high polarization photocathodes. |
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T00.00079: Strong signature of Landau level fan from high order moiré pattern in double aligned graphene heterostructures Feixiang Xiang, Abhay Gupta, Andrey Chaves, Kenji Watanabe, Takashi Taniguchi, David Neilson, Francois M Peeters, Milorad V Milosevic, Alex R Hamilton The moiré pattern in graphene heterostructures provides a great opportunity to study the energy spectrum of moving charge carriers in both a periodic potential and a magnetic field, the famous Hofstadter energy spectrum. Because of the suitable length scale of the periodic potential induced by the moiré pattern, it become possible to use laboratory accessible magnetic field to measure the Hofstadter energy spectrum. However, as the maximum periodicity of the moiré pattern in graphene heterostructures is approximately 14 nm, so far the measurable Hofstadter energy spectrum is limited to the first Bloch band. In this work, we report the transport measurement of double aligned graphene heterostructures. We observe strong signature of Landau level fan of a second order moiré pattern due to the interference of the moiré patterns from top and bottom graphene surfaces. The periodicity of the second order moiré pattern is about double the maximum periodicity of moiré patterns in graphene heterostructures. Our work indicates the second order moiré pattern in graphene heterostructures may make it possible to measure the high Bloch bands in Hofstadter energy spectrum. |
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T00.00080: Topological mechanics in rigid mechanical metamaterials Fernando E Vergara, Claudio Falcon, Carlos Cardenas Mass-spring systems have been widely studied in recent years, where isostatic systems stand out. In these systems there is a delicate balance between degrees of freedom and constraints, however the materials are usually more rigid, so it is important to study the case where the constraints exceed the degrees of freedom, or hyperstatic systems. In this work, two problems in hyperstatic systems are addressed, taking as reference systems and results previously found in isostatic systems. In the first place, the topological protection of states at finite frequency, of systems composed of isostatic and hyperstatic parts, is studied, based on topological characterizations previously described in the literature. In this work, the predominance between invariants in multiple systems is compared. On the other hand, in the nonlinear regime, the existence of a soliton in a one-dimensional system is shown, previously studied in the isostatic case. It is shown that said soliton can prevail in the hyperstatic case under certain requirements to the new restrictions. In both problems, numerical and experimental results are presented that show the possibility of extending some results from isostatic systems to hyperstatic systems. |
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T00.00081: Finite-temperature Lindhard function for α--T3 materials Danhong Huang We have calculated the static and finite-temperature Lindhard function from a general polarization function Πφ(0)(q, ω | T) in the static limit ω --> 0 for α--T3 materials with an arbitrary hopping parameter 0 < α < 1. Our results are obtained in the form of semi-analytical expressions, i.e. one of the two required integrals has been performed analytically, leading to an analytical function. The other integral, however, could be computed explicitly in the limit of either low or high temperature, including the limit of T --> 0. Physically, the static-limit polarization function is a very important quantity for calculating Boltzmann transport, electron elastic scattering, and the static screening of electrons in any newly discovered two-dimensional material. Importantly, we have recovered our previously acquired analytical expressions for graphene and for a dice lattice as α --> 0 or α --> 1, respectively. |
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T00.00082: Superhard Novel Ternary B-C-N Materials using Microwave Plasma Chemical Vapor Deposition Kallol Chakrabarty, Paul A Baker, Cheng-Chien Chen, Shane A Catledge Diamond is the hardest known material but is limited by high cost and is prone to oxidation at temperatures above 800 °C which make it unaffordable and unfavorable for many applications. Materials based on the light elements of carbon, nitrogen, oxygen, and boron can form short covalent bonds, making the structures superhard and difficult to compress or distort. Due to the vast phase space of possible element combinations, it remains challenging to explore new superhard ternary materials. In this work, Microwave Plasma Chemical Vapor Deposition (MPCVD) has been used to synthesize superhard novel ternary B-C-N coatings on silicon substrates. X-ray photoelectron spectroscopy and Fourier-transformed infrared spectroscopy confirm the B-C, C-N, and B-N bonding in the synthesized coating. Rietveld refinement of the experimental X-ray diffraction pattern was performed using the recently invented theoretically predicted novel BC10N structure by our group, and it agrees with the experimental data. BC10N can be a better choice for extreme environments, space missions, medical applications, ballistic armor, cutting tools, high-temperature electronics, MEMS applications, and many more for its superior properties. |
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T00.00083: Germanene structure enhancement by adjacent insoluble domains of lead Ting-Yu Chen, Shu-Jung Tang, David Mikolas, Woei Wu Pai The discovery of graphene has spurred great interest in the growth of a monatomic layer with a honeycomb lattice, the analogs of which belong to the family of two-dimensional (2D) Xenes. However, from the experimental side, 2D Xenes must be grown on a substrate, which usually hinders the formation of a freestanding Xene, leaving the epitaxial growth of 2D Xenes with high lattice quality and intrinsic electronic structures a tremendous challenge. |
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T00.00084: Chemical Reactivity at Mo/CuO Interface Anil R Chourasia The technique of x-ray photoelectron spectroscopy has been used to investigate the chemical reactivity at the Mo/CuO. Thin films of molybdenum were deposited on CuO substrates kept at room temperature by the e-beam method. The thickness of the molybdenum film was varied between 3 Å and 10 Å. The molybdenum 3d, oxygen 1s, and copper 2p regions were investigated. The spectral data show the absence of the high binding energy satellite in the copper 2p regions. This corresponds to the reduction of CuO to elemental copper. The molybdenum overlayer is observed to get oxidized to MoO3. The thickness of oxidized molybdenum was found to depend upon the initial thickness of the molybdenum overlayer. The reaction is observed to continue until the molybdenum overlayer exceeds a thickness of 7 Å. Beyond this thickness unreacted molybdenum is observed. The width of the interface has been estimated from the spectral data. The study provides a means of preparing nano-dimensional MoO3. |
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T00.00085: Analyzing the Resistivity Size Effect of Ruthenium Nanowires Maximillian Daughtry This poster summarizes results from recent experiments designed to characterize changes in resistivity as single-crystalline Ru(0001) terminated sheets and nanowires are progressively scaled down in thickness and wire length, respectively. Sheet resistivities are shown to obey size-dependent trends described by a semiclassical model developed by Fuchs and Sondheimer to account for contributions arising from surface scattering relative to those resulting from phonon interactions within the bulk of the material. Notably, low-temperature sheet conductivity measured from our samples exceeds that of conventional polycrystalline copper as thickness decreases below ~50 nm, which we attribute to the removal of grain-boundary scattering contributions and an ability to controllably create terminations resulting in near-specular surface scattering within our single-crystalline Ru sheets. Lithographically patterning these sheets to create nanowires (Plasmonics Inc.) appears to leave the devices with large defect concentrations, which weakens trends otherwise suggestive of ballistic conduction in shorter wires at lower temperatures. |
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T00.00086: Suitability of MO precursors for hybrid MBE using TGA Benazir Fazlioglu Yalcin, Roman Engel-Herbert Thin film materials have impacted many areas of research such as electronics, optics, energy generation, and storage. The phenomenal rise in the development of thin films is likely to continue as they have become the key elements of technological advancements. There are several deposition techniques producing thin films such as CVD, MOCVD, ALD, and MBE all of which require the starting materials to be in the gas form during growth. An alternative technique, hybrid molecular beam epitaxy (hMBE), which has been demonstrated to provide superior control over cation stoichiometry by accessing self-regulated growth kinetics, relies on metal-organic (MO) precursors to supply the element of interest to the sample on which an epitaxial film is grown.1 In contrast to the deposition techniques such as CVD, MOCVD, and ALD where the MO precursor is supplied to the deposition reactor using a carrier gas, MBE reactor pressures are not compatible with the supply of the MOs using a carrier gas to grow functional thin films. Instead, a heated gas supply is used, and MO precursor selection becomes limited to MO precursors with sufficiently high vapor pressures.2 This makes it particularly important to know the vapor pressure curves of MO precursors of interest to determine their suitability for the hMBE approach. |
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T00.00087: Characterization of 2D Heterostructure Graphene and Transition Metal Oxides Gabriel J Fedynich Two-dimensional materials with transition metal oxide heterostructures show a growing potential for a wide amount of uses in electronics including single molecule gas detectors and transistors. Due to this rising interest, the need to further understand the material properties has become a priority. The goal of this study is to further the understanding of the electronic, magnetic and structural properties of transition metal oxides interfaced with graphene. This will be accomplished by using a pulse laser depositioning method to synthesize micro-thin layers of molybdenum-oxide (MoOx) onto a silicon wafer (Si and SiO2). Then by applying a dry transfer exfoliation technique, a film of graphene will be applied. The methods of studying the material include Raman spectroscopy for determining structural properties, IV characterization for electrical properties, Photoluminescence Spectroscopy for understanding semiconducting properties, and X-Ray diffraction for crystal structures. |
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T00.00088: Liquid Phase Epitaxy of IV-VI Topological Crystalline Insulator Ian J Mercer, Andrew Liao Topological Crystalline Insulators (TCIs) have been a valued class of materials in recent years for their ability to form symmetry-protected massless surface states. Liquid Phase Epitaxy (LPE) is a high temperature deposition technique used for growing cost-efficient 2D heterostructures, while still maintaining crystalline quality and low dislocation density. Growth with LPE can become difficult due to high temperature and no vacuum. LPE has been commonly used for the growth of single crystal materials like GaAs, however there is limited work on lead salts like that of the chalcogenides and salt substrates. Here binary chalcogenide thin films have been grown with LPE and compared with more conventional methods like MBE. We found epitaxial lattice matching of binary SnTe on (111) BaF2 substrates, displaying high mobility. These results demonstrate that with specific parameters lead salts of higher thicknesses can be grown via LPE in a non-vacuum setting; implicating the quality of LPE growth vs other more expensive methods. The work thus far on SnTe LPE opens doors towards SnPbTe alloys, GeTe thin films, and even superlattices. Furthermore, highlighting that LPE can contribute to novel alloys and superlattices of lead salts. |
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T00.00089: Effect of Substrate Pre-treatment on Growth of Ultra-thin Bi2Se3 Films. Saadia Nasir, Stephanie Law, Walter J Smith, Thomas E Beechem Bi2Se3 is a widely-studied topological insulator due to its potential applications in optics and spintronics. When the thickness of Bi2Se3 is reduced to below 6 nm, the wavefunctions of the electrons on the top and bottom surfaces couple, and a small non-trivial gap opens at the Dirac point. The film then acts as a quantum spin Hall insulator. To explore this state, growing coalesced ultra-thin Bi2Se3 films at a wafer scale with defined thickness is critical. We explored the growth of ultra-thin Bi2Se3 films on sapphire substrates using molecular beam epitaxy. The films were characterized by room temperature Hall measurements, atomic force microscopy, and Raman mapping. We observed that depositing films directly on sapphire without any pretreatment resulted in fragmented non-coalesced films. Pre-treatment of the substrate by growing a few nanometers of Bi2Se3 and decomposing it completely resulted in coalesced films. In addition, the two-step growth method resulted in typical triangular domain morphology. Furthermore, higher growth rates and lower growth temperatures resulted in reduced surface roughness contrary to what is observed for conventional epitaxy. Overall, the growth of well-coalesced Bi2Se3 ultra-thin films with lower surface roughness makes them reliable for optical or electronic studies. |
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T00.00090: Synthesizing Janus Transition Metal Dichalchogenides by with High Controllability and Reproducibility YUE Xingyu In contrast to conventional transition metal dichalcogenides (TMDs) having the MX2 structure, Janus TMDs break mirror symmetry along vertical direction, providing a novel platform for some exciting phenomena such as piezoelectricity , enhanced Rashba effect , topological superconductivity, and intrinsic skyrmions, etc. Since the first report by Lu et al.[1] of growing Janus MoSeS by hydrogen plasma, Janus TMDs have stimulated great interest and many following works by plasma induced replacement of the top chalcogen layer[2] and directly sulfurization[3,4] have appeared. However, fabricating Janus structures by a more controllable approach with high reproducibility is essential for their applications, which remains challenging. In this work, we report a two-step growth by well controlled plasma treatment and Tellurium passivation to gradually synthesize Janus MSeTe (M=Mo,W) under ultrahigh vacuum condition. We employ reflection high-energy electron diffraction (RHEED) to monitor the whole fabrication process of Janus MSeTe. Piezoelectric force microscopy (PFM) measurements reveal large vertical piezoelectricity. X-ray photoelectron spectroscopy (XPS), low-energy electron diffraction (LEED) and scanning transmission electron microscopy (STEM) reveal its chemical composition and atomic structures. |
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T00.00091: Enhanced electrostatic dust removal from solar panels using transparent conductive nanotextured surfaces Fabian J Dickhardt, Sreedath Panat, Kripa K Varanasi Dust accumulation on solar panels is one of the biggest operational challenges faced by the photovoltaic industry. Removing dust using water-based cleaning is expensive and unsustainable. Dust repulsion via charge induction is one of the most promising ways to clean solar panels and recover power output without consuming a single drop of water. However, it is still challenging to remove small particles <30 because Van der Waals force of adhesion dominates electrostatic force of repulsion. Here we propose nanotextured, transparent, electrically conductive glass surfaces to significantly enhance electrostatic dust removal in the small particle size regime. We performed AFM pull-off force experiments and demonstrate that nano-textured surfaces reduce the force of adhesion by up to 2 orders of magnitude. We show that the reduced adhesion results in significantly better (~3.5x) small particle electrostatic dust removal compared to plain or micro-textured surfaces. We fabricate transparent, electrically conductive, nanotextured glass that can be retrofit on solar panel surfaces using copper nano-mask based scalable nanofabrication technique and show that we can recover > 99% of lost power output for particles >30 and recover > 90% of lost power output in the small particle regime. |
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T00.00092: Anomalous Scattering Rod in Pr2NiO4.25 Krishna D Joshi, Bryan Huey, Francesco D'Acierno, Jaclyn Grace, Padraic Shafer, Werner Paulus, Zhiwei Zhang, Barrett O Wells We report on a resonant scattering study of Pr2NiO4.25. Materials with the K2NiF4 structure (214) have attracted substantial attention over recent years. Cuprate high temperature superconductors with the 214 structure such as La2-xSrxCuO4 have seen the most investigations, but similar compounds of other transition metals also have interesting properties. Nickelates of type Ln2NiO4+y (Ln = lanthanide) have unusual magnetic behavior and often charge ordering similar to cuprates. These materials can be hole-doped by both Ln site substitution and the incorporation of excess oxygen, with smaller Ln atoms leading to distortions that allow more oxygen. Samples with Ln=Pr naturally incorporate significant excess oxygen; our studies use Pr2NiO4.25. This compound is interesting both for its connections to the cuprate superconductors and for use in low temperature solid oxide fuel cells due to its high oxygen ion conductivity. Resonant scattering studies show several resonant-only peaks. Some are likely associated with complex charge order. In addition, the nominally disallowed [001] peak appears on resonance with different behavior associated with different atomic resonances. Our newest work finds a scattering rod develops over the time along (001) direction despite a surface 20° off that direction and no apparent faceting in AFM. We will discuss the resonant and non-resonant behavior of this scattering rod and its possible origins. |
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T00.00093: Investigation of water repellency of polytetrafluoroethylene surface by plasma etching KIWOONG KIM Fabrication of superhydrophobic surfaces (SHS) is important in many fields owing to their excellent advantages such as anti-freezing, corrosion prevention, and self-cleaning. However, to modify the surface structure, environmental pollution caused by complex processes and chemical treatment must be considered. In this study, the surface of polytetrafluoroethylene (PTFE) was plasma-treated using oxygen and argon to change the surface structure without a complicated process. The PTFE surface was treated in two ways: plasma etching (PE) and reactive ion etching (RIE). The contact angle of the pristine PTFE surface was 113.8±1.4°, but the contact angle of the surface manufactured by PE and RIE was 152.3±1.7° and 172.5±1.2°, respectively. The shape of the liquid collision was observed, and the water repellency was confirmed by calculating the contact time. The contact time of the PE specimen was 24 ms longer than that of the RIE specimen, and the RIE specimen was only 18 ms. When the self-cleaning effect was confirmed using graphite, the RIE specimen exhibited an excellent self-cleaning effect, and most of the graphite on the surface was removed within 20 s. We believe that the SHS fabricated by plasma etching method using safe gases can be a good candidate to develop tip-like polymer nanoarrays with special performances in a simple process. |
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T00.00094: Crystal Facet Energies and Surface Reconstructions in Spinel MgV2O4 Nanocrystals Francisco J Lagunas Vargas, Adriana L Punaro, Grant C Alexander, Christian Moscosa, Jordi Cabana-Jimenez, Robert F Klie Spinel vanadium oxides are promising candidate material for multivalent ion battery cathodes. In MgV2O4, the spinel framework provides ionic pathways for the migration and reintroduction of Mg2+ upon electrochemical cycling. These pathways are highly directional, in the case of spinels oriented parrallel to [110] and symmetric surface types, thus the overall crystal shape and size play an important role in cathode design. |
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T00.00095: A facile structural engineering of porous coordination polymers for enhanced gas separation performance Jong Suk Lee, Heseong An, Ki Jin Nam, Jung Ho Seong, Won Seok Chang Membrane-based gas separation technique is attractive due to its good energy efficiency and small footprint. Especially, polymeric membranes incorporated with homogeneously distributed nanofillers, called mixed matrix membranes (MMMs), are an attractive platform owing to potential scalability and excellent molecular size/shape-sieving ability. However, several technical challenges, including the fine-tuning of molecular structures and the suppression of interfacial voids between polymer and nanofillers should be addressed for industrial applications. Zeolitic imidazolate frameworks (ZIFs) are attractive porous coordination polymers constructed from zinc metal ions and organic ligands for gas separations. The purpose of the current study is to engineer the desired molecular structure of ZIF nanofillers for enhanced gas separation performance. A facile defect engineering is proposed to suppress the formation of non-selective interfacial voids around nanofillers and enhance the molecular sieving behaviour of ZIFs by introducing Zn-alkyl amine coordination into the framework. In addition, the fine-tuning of molecular structures of ZIF nanofillers is realized either by in-situ synthesis or by post-synthetic modification for excellent gas separation performance. |
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T00.00096: Evaluation of the structural changes at a surface level of low and medium carbon steel due to the use and effect of TiO2 and MnO nanoparticles. Jair Olvera, CONCEPCION MEJIA GARCIA, Ana María Paniagua Mercado, Antonio Silvio De Ita de la Torre, Jaime Santoyo Salazar, Everardo Miguel Díaz Several cuts of a low (ASTM A36) and medium (SAE 1045) carbon steel plate were made to prepare different samples of size 10.16x5.08x1.27 cm, which were polished on the upper face; to eliminate the oxidizing material and polluting residues. Each sample was covered with different nanoparticles on the surface. Five different types of nanoparticles with different sizes were used. We have four oxides: TiO2 (21 nm) and MnO (50 nm). Each sample was placed in a steel hearth box with a lid; each box, in turn, was introduced into a muffle to carry out heat treatment at 950 °C for 24 hours. |
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T00.00097: Magnetic atom chain platform for Majorana fermions Yawen Peng Magnetic atom chains on the surface of a conventional superconductor provide a novel approach to realize a topological superconductor, which host Majorana fermions at the edge of 1D chains. Here we report a self-assembled magnetic atomic chain structure on a two dimensional (2D) superconductor, which provides a platform for future research on the Majorana fermions. We grow the helimagnet Mn1/4TaS2 single crystal, which is Mn atoms intercalated into the vdW gaps of 2H-TaS2 to form an ordered lattice. Using scanning tunneling microscope, we confirm the 2x2 Mn superstructure, and magnetic Mn atom chains on the surface after in situ cleaving. This self-assembled behavior is temperature dependent, that Mn atoms show 2x2 periodicity when cleaved at low temperature, while form atomic chains when cleaved at room temperature and annealed at higher temperature. With careful selection of annealing temperature and time, isolated chains can be obtained and are promisng for the formation of a topological phase and Majorana fermions. |
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T00.00098: Towards A Multiscale Model Of Aluminum Corrosion: Assessing The Strength Of Protective Oxide Films Jeremy A Scher, Tae Wook Heo, Stephen Weitzner, Yue Hao, Stephen T Castonguay, Sylvie Aubry, Matthew P Kroonblawd Aluminum metal reacts readily with the environment and forms a nanometer-scale protective oxide/hydroxide film at the surface. Once formed, these films greatly reduce further corrosion by shielding the bare metal underneath. Fracturing of the protective film can expose the metal, accelerating corrosion chemistry. Information about the strength properties of these materials can be leveraged by component-scale predictive lifetime models to make more refined predictions about net reaction kinetics. In this work, we use molecular dynamics with a reactive force field to calculate the stress response of bulk aluminum oxide and hydroxide under uniaxial deformation for various boundary conditions and strain rates. The inclusion of crystal defects such as grain boundaries and porosity and their effects on material response to deformation are also considered. |
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T00.00099: Compressive deformation of a translucent material containing an opaque contrasting filler as a pressure indicator mechanism Justin D Smith, Ali Ammar, Wafa Tonny, Samuel Wallaert, Venkatesh Balan, Megan L Robertson, Alamgir Karim Many strategies have been developed for pressure-indicating materials due to their importance in areas such as monitoring of structural integrity, impact analysis, and food processing. The prevailing technology for pressure-indicating films has its origins in the development of microcapsule-based carbonless copy paper in the mid-20th century, but this approach suffers from material and chemical complexity, non-continuous response, and limited sustainability. In this work, an overlooked mechanism for pressure-responsive color change is demonstrated using cellulose acetate membranes prepared by direct immersion annealing with different loadings of activated charcoal. Compressive plastic deformation of the translucent cellulose acetate leads to a decrease in optical path length and a concomitant increase in the visibility of the opaque contrasting filler. Membranes were characterized by ATR-FTIR, TGA, cross-sectional SEM, AFM, optical microscopy, and gas adsorption properties. A linear relationship between applied pressure and resultant pressure mark brightness in the range of 12–56 MPa was observed for membranes bearing 1–7 wt% activated charcoal. Comparison of pressure mark patterns with cross-sectional SEM supports the importance of the direct-immersion-annealing-based porous morphology for the tuning of indicator sensitivity and dynamic range. A simple drop test was used to illustrate the robustness and utility of these indicators in optical impact assessment. |
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T00.00100: Suppression of potassium dendrite via surface control of substrate Sung-Hyun Jie, Byeongyong Lee, Seunghwi Baek With its abundance and low redox potential, potassium (K) is considered as the most promising anode material for next-generation rechargeable batteries. However, due to the highly reactive nature of K in the electrolyte, irregular electrodeposition of K leads to continuous dendrite growth, resulting in poor electrochemical performances. Herein, structurally and chemically defected crumpled graphene (d-CG) is used as the host material to suppress dendrite growth and reduce overpotential. The defects on d-CG are highly potassiophilic which homogenize K ion flux and local current density. As a result, d-CG represents a dendrite-free morphology during K plating/stripping and high electrochemical performance. d-CG shows high coulombic efficiency (CE) while copper foil exhibits lower CE. In addition, in a half cell (K||d-CG), d-CG electrode represents significantly lower overpotential at 110mV than that of K (160mV). By virtue of defect effects on dendrite control, stable K metal batteries are realized. This study provides a step forward for K metal batteries. |
Author not Attending |
T00.00101: Ab-initio Investigation of Hydrogen and Helium Behavior Near W/ZrC Interfaces Geeta Sachdeva Efforts to improve the thermomechanical properties of plasma-facing materials when exposed to high-energy particle irradiation led to a new class of materials; dispersoids strengthened W. For example, carbide-dispersion strengthened W has been shown to improve ductility, crack resistance, and radiation tolerance. Here we discuss various aspects of W-ZrC interfaces leading to their stabilities and focus on how these features impact the H/He behavior at and near the interface. Our results indicate that ZrC (111) –W (110) exhibits the highest adhesive energy compared with the other investigated interfaces and hence forms the most stable interface. The impurities hydrogen and helium tend to segregate to the interfaces, which can both embrittle the interface and potentially increase gas retention. In addition, the interface could facilitate the diffusion of hydrogen and helium by providing a low-barrier channel. The present work can provide key mechanistic insights towards interpreting recent experimental studies of the interface structure and H/He retention in W-ZrC interfaces and guide the design of future W-based materials for improving plasma-facing component performance in fusion energy applications. |
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T00.00102: The Effect of Hydrogen, Hydroxyl, and Oxygen Surface Coverage on Structural and Electronic Properties of Diamond (100) Surfaces Jenille Cruz, Dmitry Ruzmetov, A. Glen Birdwell, Elias Garratt, James Weil, Pankaj Shah, Tony Ivanov, Michael Groves, Mahesh R Neupane Diamond has unique structural, thermal, and electronic properties that make it an interesting material for many device applications that operate in extreme conditions, such as radio-frequency field-effect transistors, power amplifiers, and communication satellites. To utilize the unique surface dependent electronic properties of the diamond surface, a comprehensive understanding of the surface adsorbate types and coverage is required. In this study, we performed Density Functional Theory (DFT) calculations of diamond (100) surfaces terminated with various percent coverages of H, OH, and O in ketone configuration (Oketone), and O in ether configuration (Oether). Between 25 to 75% coverages, Oketone, where the O atom is doubled bonded with the surface C atom, was the most favorable. At 100% coverage, Oether, where the O atom is bridged between the two surface C atoms, was the most favorable. Analysis of the electronic properties revealed that at 100% coverage, Oketone had the smallest bandgap, followed by Oether, H, and OH. Combinations of OH, Oketone, and Oether mixed with H produced a range of electronic properties that can provide flexibility in designing diamond-based devices. Overall, having various degrees of surface coverage of different functional groups terminated on the surface leads to the modification of electronic properties for engineering diamond surfaces. |
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T00.00103: Enhancement of Surface Second Harmonic Generation in Noncentrosymmetric Crystals Mojgan Dehghani, Jiandi Zhang, Louis H Haber Second harmonic generation (SHG) is an optical technique to probe a variety of surface and interface properties of materials with a submonolayer sensitivity. In media with inversion symmetry, SHG is forbidden within the bulk due to the electric dipole approximation while at the surface, the inversion symmetry breaks by material discontinuity, and the SHG is allowed. In crystals without inversion symmetry, electric-dipole transitions are allowed. Therefore, both the surface and the bulk contribute to the SHG radiation. However, the SHG responses are largely dominated by the intense bulk contribution and the weak surface response is ignored in many studies. We demonstrate that a femtosecond amplifier laser can enhance the surface SHG contributions. In particular, we introduce two incident power regimes where the fundamental light is generated by either an amplifier laser or an oscillator laser. We study the reflected SHG signal from two non-centrosymmetric crystals, GaAs (001) and GaP (001), as a function of azimuthal rotation angle under different polarization geometries of the fundamental and SHG waves. Our results from these two independent laser source investigations reveal that in the oscillator regime, the SHG signal originated from the bulk predominates and the surface response is exceedingly small. Under the same experimental conditions, the amplifier regime manifests strong surface SHG contributions compared to the oscillator regime. |
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T00.00104: Molecular dynamics and DFT simulations on the effect of impurities and metallic dopants on the strength of Cu grain boundaries. Vasileios Fotopoulos, Corey S O'Hern, Alexander Shluger Non-metallic impurities introduced in metals during deposition along with metallic dopants are expected to affect the properties of grain boundaries (GBs) and, thus, can be detrimental to the performance of the material [1]. However, the exact effects that these elements can have on the properties of the GBs are not yet fully understood. Moreover, simulations of such systems using quantum mechanical approaches are constrained to models with less than 1000 atoms. |
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T00.00105: Measuring the phonon contributions to total thermal conductivity of Ruthenium and Tungsten thin films using a steady-state thermoreflectance technique Md Rafiqul Islam, Sean W King, Kandabara Tapily, Daniel H Hirt, John Tomko, Christopher Jezewski, Colin D Landon, Kiumars Aryana, Colin Carver, Patrick Hopkins, Eric R Hoglund, Rinus T.P. Lee The total thermal conductivity of a metal is the sum of the electronic thermal conductivity and the phonon thermal conductivity, along with any other heat carriers if they exist. Typically we assume that phonon thermal conductivity is negligible for metals, however, this hypothesis has not been subjected to stringent experimental validation due to difficulties in measuring phonon thermal conductivity. In this work, we study the phonon and electron contribution to the thermal conductivity of ruthenium (Ru) and tungsten (W) films scale at nanometer dimensions via independent measurements of the thermal and electrical transport properties. We perform sheet resistance and thermoreflectance-based nanoscale thermal conductance measurements on Ru films ranging from 20 to 100 nm thick and W films ranging from 20 to 30 nm thick, deposited by the physical vapor deposition (PVD) method. We obtain the electrical resistivity with the four-point probe method and then calculate in-plane thermal conductivity employing the Wiedemann-Franz (WF) law and the bulk metal's Lorenz number. We directly measure the in-plane thermal conductivity of the Ru and W thin films via steady-state thermoreflectance technique. The in-plane thermal conductivity of these thin films measured with thermoreflectance-based method is at least 15% higher than the WF law-derived thermal conductivity. This indicates the viability of thermoreflectance-based method in capturing the phonon contributions to the total thermal conductivity of metals which the sheet resistance method can not measure. |
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T00.00106: Necessary Interface Characteristics for Elecronic Growth on Layered Dichalcogenides Tim E Kidd, Andrew J Stollenwerk, Pavel Lukashev, Colin Gorgen, Jeff Carlson Under very specific conditions of metallic film growth, the electronic characteistics of the metal can play a deciding role in determing the structural properties of the film. This electronic growth, which can be harnessed to create self assembled quantized nanostructures or films of discrete thickness, is quite uncommon. Normally, electronic energy considerations are quite weak compareed to standard growth paramteres like straing, bonding energies, surface mobility, and surface free energy. In recent years, we hace discovered that certain metals will exhibit electronic growth when deposited upon the surfaces of layered dichalcogenides. The electrnic growth can occur well above room temperature, showing a high defree of stability even though lattice mismatch in these systems is about 10%. We have cplored different characterstics related to bonding conditions for different metals and substrates to their growth properites. We find that a high degree of surface mobility is a good indicator for potential electronic growth, and that the bonding site is also important. In adddition to mobility, we believe that having a small energy difference between multiple surface bonding sites is also important for alleviating strain to enable electrnic growth. Some level of disorder at the interface layer seems seems to minimize the total energy so that the metal films can achieve bulk-like configurations even at nanometer scale thicknessses. This work can be used to spontaneously create nanostructures or thin films for use in catalysis or as substrates for the study of self assembled monolayer systems or surface enhanced Raman spectroscopy. |
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T00.00107: Rotation of the misfit dislocation grid as a function of the thickness in epitaxial FeSe thin films Zheng Ren, Hong Li, He Zhao, Shrinkhala Sharma, Ilija Zeljkovic Misfit dislocations appear in epitaxially-grown films and serve as a strain-relief mechanism. Previously, well-ordered dislocation grids have been observed in rock-salt structure films grown on substrates with a similar lattice structure, for example, PbTe/PbSe. Here, we use molecular beam epitaxy to synthesize FeSe thin films on a disimilar substrate SrTiO3. Using low temperature scanning tunneling microscopy, we observe well-ordered misfit dislocation networks in multilayer FeSe films. Surprisingly, the orientation of the dislocation network rotates by 45 degree from the 4 monolayer thick film to the 8 monolayer thick film. Moreover, a secondary grid is found in the 4 monolayer dislocation network which has the same orientation as the 8 monolayer network. Interestingly, the spacing of the secondary grid can be nicely fitted with the Matthews-Blakeslee model. The origin of the rotation of the dislocation networks will be discussed. |
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T00.00108: Surface Segregation in Fe-Ge Thin Films Jack L Rodenburg, Gauthami Viswan, Mohammad Z Zaz, Esha Mishra, Thilini K Ekanayaka, WaiKiat Chin, Peter A Dowben, Robert Streubel Angle-resolved X-ray photoemission spectroscopy (XPS) has been used to study the surface composition of Fe-Ge thin films. The surfaces of Fe-Ge thin films have not been studied extensively but conclusion here is that under some circumstances, Fe-Ge thin films favor iron segregation to the surface in spite of the larger moment of Fe. A model has been developed to assist in the analysis of the experimental angle-resolved XPS data to construct a more quantitative picture of the surface composition and surface enthalpies. The XPS spectra are indicative of interactions between Ge and Fe arguing against an alloy with strong clustering. Si capping layers have pin-holes that can lead to limited oxidation. |
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T00.00109: Antagonism between polar displacements and Rashba phenomena in strained SrTiO3 Julien Varignon, Manuel Bibes, Laurent Vila, Jean-Phillippe Attane Spintronic exploits the spin degree of freedom in addition to the charge of carriers, yielding numerous applications in data storage for instance [Nat. Mater. 6, 813 (2007)]. An alternative pathway toward lower power spintronics exists and exploits the spin-orbit interaction (SOI) of non-magnetic materials through the Spin Hall Effect (SHE) [Phys. Lett. 13, 467 (1971); Science 306, 1910 (2004)] and inverse Spin Hall Effect (ISHE) Nat. Commun. 3, 629 (2012); Phys. Rev. Lett. 96, 246601 (2006)]. More recently, a promising pathway toward efficient spin-charge current interconversion has been identified and uses a peculiar interplay between polar displacements and SOI: when inversion symmetry is broken, such as at interfaces, surfaces or in ferroelectric compounds, the polar displacements can yield a Rashba interaction lifting the degeneracy of bands according to their spin [JETP Lett. 39, 78 (1984)]. The efficiency of the conversion is related to the Rashba parameter, usually assumed to depend directly on the spin-orbit interaction and polar displacements amplitude. |
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T00.00110: "Effects of X-ray Exposure on the Physical Characteristics of Metallic Thin Films" Dorothy E Doughty This experiment is designed to understand the impacts of broad spectrum radiation on metallic films with emphasis on corrosion resistance. There was an analysis of depositions of films on a silicon substrate: Copper, Titanium, Titanium Nitride, Silver, and Aluminum. These depositions were analyzed through Scanning Electron Microscopes and Energy Dispersive X-ray Spectroscopy then irradiated through a rhodium source. These atomic compositions of these samples were compared before and after x-ray exposure and determined to have an increase in oxygen composition. These x-rayed films underwent a series of acid etching tests and the x-rayed samples had an increased resistivity to corrosion. The resistivity was visual in decreased pitting in the films. The composition of the oxide layer was analyzed through the SEM. This experiment showed an increase in oxygen content for all materials irradiated with a rhodium source. Evidence suggests x-rays induced an ionization reaction at the surface which creates an oxide layer for all materials investigated. In most instances, the oxide layer forms a corrosion resistant surface layer. Limited evidence suggests an improvement in adhesion resulting from oxygen availability at the coating and substrate interface. |
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T00.00111: Epitaxial growth and characterization of Cu single crystalline films suitable for creation of ballistically conducting nanojunctions Ahmed R Hegazy, Quintin Cumston, Maximillian Daughtry, William Kaden, Kevin Coffey Continued downscaling of Cu nanostructures relevant to CMOS interconnects has been impractical due to resistivity size effects, which result in competitively disadvantageous wire conductance relative to other metals below device length scales of ~10 nm size. Recent publications by our group have shown an ability to controllably minimize grain boundary and surface scattering contributions to resistivity measured through epitaxially grown Ru/Al2O3(0001). Moreover, unpublished work by our group now suggests evidence of ballistic conduction through ~100 nm long nanowire devices lithographically produced from such sheets. A similar approach might be expected to allow for ballistic transport through longer devices as a result of improved mean free path for electron scattering through copper vs. ruthenium. This presentation provides results obtained from Cu films grown on MgO(100) and CaF2(100). MgO-supported film growth is done at the wafer scale using approaches already established at smaller scales under better controlled conditions, while CaF2 studies will be completed in situ within a UHV surface-science chamber. Key results includes: film thickness and structure characterization (XRR, XRD, and LEED), chemical-state analysis (XPS) and sheet resistance measurements as a function of deposition and processing conditions. |
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T00.00112: Statistical complexity and the structure of multi-qubit entangled states Manuel H Munoz Arias, Anupam Mitra Multi-qubit states and their entanglement structure have been of central importance to recent developments in quantum information science and condensed matter. In this work, we investigate the structure of pure multi-qubit entangled states under the lens of statistical complexity and the entropy-complexity (EC) plane. A concept and a tool well known in the domain of complex systems, in particular, time series analysis. This tool permits the construction of a low-dimensional representation of and, in principle, arbitrarily high-dimensional probability space. At the same time, and for a given value of the entropy, allows for the identification of high and low complexity probability vectors, thus defining a classification for these objects. Exploiting this conceptual framework and methodology, we characterize several well known multi-qubit states based on the EC coordinates of their subsystem marginals. We also investigate the structure of eigenstates of many-body Hamiltonians and their out-of-equilibrium dynamics. In the later case we focus on the comparison between local equilibration and decoherence. Finally, as a complementary application of the method, using the diagonal ensemble, we take a look into the road to equilibrium for a paradigmatic example of a many-body chaotic Hamiltonian and present a clear separation between quantum dynamics and dynamics driven by random Hamiltonians, which, nevertheless capture the system properties at equilibrium. |
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T00.00113: Computing the Many Body Density of States of a system of non interacting identical quantum particles Gregoire Ithier, Rémi Lefèvre, Krissia d Zawadzki The modeling of many-body (MB) quantum systems undergoing an out-of-equilibrium evolution |
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T00.00114: Transport in a periodically driven system using the extended reservoir approach Gabriela M Wojtowicz We extend the approach based on extended reservoirs to quantum transport with time-dependent Hamiltonian. We characterize the convergence for time dependent models in range of driving frequency in a case of Markovian and non-Markovian reservoirs. In our work we describe specific aspects of the approach for problems with periodic driving and we suggest the strategy to define optimal relaxation rate. |
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T00.00115: Heating suppression for random driving Hongzheng Zhao, Roderich Moessner, Johannes Knolle, Florian Mintert, Takashi Mori, Mark Rudner Driven quantum systems may realize novel phenomena absent in static systems, but driving-induced heating can limit the timescale on which these persist. We study heating in interacting quantum many-body systems driven by random sequences with n-multipolar correlations, corresponding to a polynomially suppressed low-frequency spectrum. For non-zero n, we find a prethermal regime, the lifetime of which grows algebraically with the driving rate, with exponent 2n+1. A simple theory based on Fermi's golden rule accounts for this behavior. The quasiperiodic Thue-Morse sequence corresponds to the infinite n limit. Despite the absence of periodicity in the drive, and in spite of its eventual heat death, the prethermal regime can host versatile nonequilibrium phases, which we illustrate with a random multipolar discrete time crystal. I will also discuss the drive-induced particle excitation to higher bands which commonly occurs in experimental setups. These higher bands effects turn to be controllable even away from a high-frequency driving regime. This opens a window for observing drive-induced phenomena in a long-lived prethermal regime in the lowest band. |
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T00.00116: Anisotropic quantum transport through a diatomic molecule trapped in a nanojunction Elvis F Arguelles, Koji Shimizu Small molecules trapped in nanojunctions have been serving as toy models for the study of many interesting physical phenomena such as quantum tunneling and tunneling-induced light emission to name a few. In previous works, the resonance width due to coupling with leads has been taken as a constant parameter, independent of the scattering region’s orientation. In this work, we describe the electron hopping between metal electrodes and a diatomic molecule microscopically, explicitly considering the molecule’s orientation in the nanojunction. Using the Keldysh formalism and parameters derived from first principles calculations, we show that the quantum transport through the diatomic molecule is highly anisotropic. The spectral function significantly broadens or sharpens depending on the molecular orientation with respect to the axis of the metal leads, which subsequently affects the current. Further, by taking the rotational average of the tunneling matrix elements, we obtain the rotational-state-dependent quantum transport properties. |
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T00.00117: Probing real-time broadening of nonequilibrium density profiles via a local coupling to a Lindblad bath Tjark Heitmann, Jonas Richter, Jacek Herbrych, Jochen Gemmer, Robin Steinigeweg The Lindblad master equation is one of the main approaches to open quantum systems. While it has been widely applied in the context of condensed matter systems to study properties of steady states in the limit of long times, the actual route to such steady states has attracted less attention yet. Here, we investigate the nonequilibrium dynamics of spin chains with a local coupling to a single Lindblad bath and analyze the transport properties of the induced magnetization. Combining typicality and equilibration arguments with stochastic unraveling, we unveil for the case of weak driving that the dynamics in the open system can be constructed on the basis of correlation functions in the closed system, which establishes a connection between the Lindblad approach and linear response theory at finite times. This connection particularly implies that closed and open approaches to quantum transport have to agree strictly if applied appropriately. We demonstrate this fact numerically for the spin-1/2 XXZ chain at the isotropic point and in the easy-axis regime, where superdiffusive and diffusive scaling is observed, respectively. |
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T00.00118: Analyticity constraints bound the decay of the Spectral Form Factor Pablo Martinez-Azcona, Aurelia Chenu Quantum chaos cannot develop faster than λ≤ 2π/β for systems in thermal equilibrium [Maldacena, Shenker & Stanford, JHEP (2016)]. This `MSS bound' on the Lyapunov exponent λ is set by the width of the strip on which the regularized out-of-time-order correlator is analytic. We show that similar constraints also bound the decay of the spectral form factor (SFF), that measures spectral correlation and is defined from the Fourier transform of the two-level correlation function. Specifically, the inflection exponent η, that we introduce to characterize the early-time decay of the SFF, is bounded as η≤ π/(2β). This bound is universal and exists outside of the chaotic regime. The results are illustrated in systems with regular, chaotic, and tunable dynamics, namely the single-particle harmonic oscillator, the many-particle Calogero-Sutherland model, an ensemble from random matrix theory, and the quantum kicked top. The relation of the derived bound with other known bounds, including quantum speed limits, is discussed. |
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T00.00119: Power of deep convolutional recurrent networks in predicting the dynamics of random quantum circuits Naeimeh Mohseni Machine learning has shown significant breakthroughs in the field of quantum computing in particular deep neural networks exhibited remarkable power in enhancing quantum many-body dynamical simulations. In this work, we study the connection between the power of data-driven deep networks in learning the dynamics of physical observables of quantum many-body systems and the way that quantum information scramble with a focus on the random quantum circuits. In particular, utilizing convolutional recurrent neural networks we study how the extrapolation power of the neural network in time and system size where the network has not been trained is correlated with the localization of quantum information in the system. We illustrate integrability can be used as a figure of merit to identify the power of deep neural networks in extrapolating the predictions. |
Author not Attending |
T00.00120: Enhancing spin-spin correlations in the mixed-field Ising model with stochastic resetting Vladimir Ohanesjan, Irina Petreska, Trifce Sandev Recently was discovered that stochastic resetting in quantum systems may lead to the emergence of non-trivial correlations, even in the absence of intrinsic interactions. Here, we are interested in the mixed-field Ising (MFI) model subject to stochastic resetting, a protocol that interrupts the unitary evolution by returning the system to its initial state. We analyze analytically the two-point transverse correlations σixσjx , in the limit without nearest neighbor interactions which reduces the system to an ensemble of Two-Level Systems (TLS), when being reset to the ferromagnetic state with maximal magnetization and find nontrivial resetting induced correlations. For a specific magnitude of the transverse field, the two-point transverse correlations reach a maximum, and increasing the field further only decorrelates the system. To obtain a deeper insight into the maximum of the correlations, we analyzed their dependence on both, the resetting rate and the external fields. Furthermore, using numerical techniques we study analytically inaccessible realizations of MFI, like the chaotic regime, and explore the effects of resetting on the internal unitary dynamics. Our results suggest that the two-point transverse correlations can be fine-tuned by the stochastic resetting and we concluded that some optimal range exists for the resetting rate parameter, which enhances those correlations. |
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T00.00121: Spatiotemporal dynamics of classical and quantum density profiles in low-dimensional spin systems Tjark Heitmann, Jonas Richter, Fengping Jin, Kristel Michielsen, Hans De Raedt, Robin Steinigeweg We provide a detailed comparison between the dynamics of high-temperature spatiotemporal correlation functions in quantum and classical spin models. In the quantum case, our large-scale numerics are based on the concept of quantum typicality, which exploits the fact that random pure quantum states can faithfully approximate ensemble averages, allowing the simulation of spin-1/2 systems with up to 40 lattice sites. Due to the exponentially growing Hilbert space, we find that for such system sizes even a single random state is sufficient to yield results with extremely low noise that is negligible for most practical purposes. In contrast, a classical analog of typicality is missing. In particular, we demonstrate that, in order to obtain data with a similar level of noise in the classical case, extensive averaging over classical trajectories is required, no matter how large the system size. Focusing on (quasi-)one-dimensional spin chains and ladders, we find a remarkably good agreement between quantum and classical dynamics. This applies not only to cases where both the quantum and classical model are nonintegrable, but also to cases where the quantum spin-1/2 model is integrable and the corresponding classical model is not. Our analysis is based on the comparison of space-time profiles of the spin and energy correlation functions, where the agreement is found to hold not only in the bulk but also in the tails of the resulting density distribution. The mean-squared displacement of the density profiles reflects the nature of emerging hydrodynamics and is found to exhibit similar scaling for quantum and classical models. |
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T00.00122: Observation of a Prethermal U(1) Discrete Time Crystal Andrew W Stasiuk A time crystal is a novel state of periodically driven matter which breaks discrete time translation symmetry. Time crystals have been demonstrated experimentally in various programmable quantum simulators and exemplify how non-equilibrium, driven quantum systems can exhibit intriguing and robust properties absent in systems at equilibrium. These states are often stabilized by prethermalization, in which a periodically driven quantum system heats to infinite temperature exponentially slowly in the driving frequency. Recent theoretical work has developed the notion of prethermalization without temperature in order to explain time crystalline observations at (or near) infinite temperature. In this work, we utilize prethermalization without temperature to conclusively verify the emergence of a prethermal U(1) time crystalline state at infinite temperature. Here we show the existence of a long-lived prethermal regime whose lifetime is significantly enhanced by strengthening an emergent U(1) conservation law. In our solid-state NMR quantum simulator, we measure this enhancement through the global magnetization, and utilize on-site disorder to measure local observables and rule out the possibility of many-body localization. We thus conclusively verify the predictions for a time crystalline state of a high temperature spin ensemble. Additionally, we investigate the response of a novel short-range correlated initial state, the dipolar order, under time crystalline driving. |
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T00.00123: Higher rank chirality and non-Hermitian skin effect in a topolectrical circuit Penghao Zhu, Xiao-Qi Sun, Taylor L Hughes, Gaurav Bahl While chirality imbalances are forbidden in conventional lattice systems, non-Hermiticity can effectively avoid the chiral-doubling theorem to facilitate 1D chiral dynamics. Indeed, such systems support unbalanced unidirectional flows that can lead to the localization of an extensive number of states at the boundary, known as the non-Hermitian skin effect (NHSE). Recently, a generalized (rank-2) chirality describing a 2D robust gapless mode with dispersion ω=kxky has been introduced in crystalline systems. Here we demonstrate that rank-2 chirality imbalances can be established in a non-Hermitian (NH) lattice system leading to momentum-resolved chiral dynamics, and a rank-2 NHSE where there are both edge- and corner-localized skin modes. We then experimentally test this phenomenology in a 2-dimensional topolectric circuit that implements a NH Hamiltonian with a long-lived rank-2 chiral mode. Using impedance measurements, we confirm the rank-2 NHSE in this system, and its manifestation in the predicted skin modes and a highly unusual momentum-position locking response. Our investigation demonstrates a circuit-based path to exploring higher-rank chiral physics, with potential applications in systems where momentum resolution is necessary, e.g., in beamformers and non-reciprocal devices. |
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T00.00124: MATERIALS PHYSICS
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T00.00125: Observation of anisotropic Dirac cones in the topological material Ti2Te2P Iftakhar Bin Elius, Gyanendra Dhakal, Firoza Kabir, Ashis Nandy, Alexandros Aperis, Anup Pradhan Sakhya, Subhadip Pradhan, Klauss M Dimitri, Christopher Sims, Sabin Regmi, Md Mofazzel Hosen, Yangyang Liu, Luis E Persaud, Dariusz Kaczorowski, Peter M Oppeneer, Madhab Neupane Anisotropic bulk Dirac (or Weyl) cones in three-dimensional systems have recently gained intense research interest as they are examples of materials with tilted Dirac (or Weyl) cones indicating the violation of Lorentz invariance. In contrast, the studies on anisotropic surface Dirac cones in topological materials which contribute to anisotropic carrier mobility have been limited. By employing angle-resolved photoemission spectroscopy and first-principles calculations, we reveal the anisotropic surface Dirac dispersion in a tetradymite material Ti2Te2P on the (001) plane of the Brillouin zone. We observe quasi-elliptical Fermi pockets at the M point of the Brillouin zone forming the anisotropic surface Dirac cones. Our calculations of the Z2 indices confirm that the system is topologically nontrivial with multiple topological phases in the same material. In addition, the observed nodal-line-like feature formed by bulk bands makes this system topologically rich. |
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T00.00126: Investigation of the thermal transport and magnetic properties of 2M-WS2 Jefferson A Carter, Joseph McBride, Brian Leonard, Jinke Tang Magnetic measurements are conducted on polycrystalline 2M-WS2 samples using a Quantum Design Physical Property Measurement System (PPMS) to confirm the superconducting Meisner effect transition at approximately 8 K. This superconducting regime is currently explored using thermal Hall measurements. Thermal Hall measurements allow for an exploration of physical phenomena present in the 2M-WS2 samples within the superconducting state. |
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T00.00127: The Elastic Moduli of 2D Transition Metal Dichalcogenides Alem A Teklu, Noah Kern, Narayanan Kuthirummal, Joe Tidwell, Max Rabe, Yu Gong The elastic moduli of four transition metal dichalcogenides (TMDs) were studied using an atomic force microscope (AFM). Nanoindentation was performed using the AFM to generate force curves which were analyzed using the Oliver-Pharr method. The TMDs tested were Molybdenum Disulfide (MoS2), Rhenium Diselenide (ReSe2), Rhenium Disulfide (ReS2), and Tungsten Diselenide (WSe2) which had a Young’s modulus values of 71.9 GPa, 28.3 GPa, 56.3 GPa, and 40.4 GPa respectively. The results are significantly lower than the expected values for the elastic moduli obtained from density functional theory (DFT) calculations. |
Author not Attending |
T00.00128: Longitudinal plasmon excitations of a model Nodal Line Semimetal Ahmed Nafis N Arafat, Oleg L Berman, Godfrey Gumbs Topological semimetals (TSM) are an increasingly studied group of symmetry protected topological phases of matter. They contain conduction and valence bands that cross each other in the Brillouin zone (BZ). This crossing cannot be eliminated by perturbation of the Hamiltonian without breaking crystalline or time-reversal symmetry. For 3D TSM, two bands may cross along a closed curve referred to as a nodal line. These TSM are referred to as topological nodal line semimetals (TNLSM). We have calculated the plasmon dispersion relation for a model 3D NLSM. We determined the polarization bubble which is then substituted into the temperature, wave number and frequency-dependent dielectric function in the random-phase approximation (RPA). The self-sustained plasma oscillations as well as their life times due to Landau damping by the single-particle excitations are determined for this model NLSM at T=0 K. The Friedel oscillations associated with impurity screening are also examined. |
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T00.00129: Antiperovskites Materials: a Playground for Magnetic and Topologically Nontrivial Effects Ranjan K Barik, Lilia M Woods The existence of Dirac and Weyl states in antiperovskite materials has opened up new opportunities to design next-generation spintronics devices. Specifically, oxide antiperovskites Eu3PbO, Eu3SnO, Yb3PbO, and Yb3SnO have unique f-electron configurations with the emergence of Weyl points near the Fermi level, making them a suitable candidate for creation and manipulation of spin-polarized electron currents. In this work, using the first-principles methods, we investigate the antiferromagnetism and ferromagnetism transition of Eu3PbO and Eu3SnO in terms of a detailed analysis of their electronic band structures and Berry curvatures. The existence of surface Fermi arcs and their specific properties for the various magnetic states are studied. Also, Yb3PbO and Yb3SnO are found to be topological insulators and non-magnetic Weyl semimetal, respectively, due to their filled f-electron shells. These materials exhibit much-enhanced spin Hall and anomalous Hall effects, which are related to their unique band structures. Our findings could offer a platform for the interplay between topological physics and magnetism to study the spintronics properties in a large class of materials. |
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T00.00130: Sum-Frequency Generation Spectroscopic studies on Multiple-Domain Weyl Semimetal CoSi (0.2 – 1eV) Si-Tong Liu, Syed Mohammed Faizanuddin, Kalaivanan Raju, Raman Sankar, Ranganayakulu K. Vankayala, Min-Nan Ou, Yu-Chieh Wen* With the spin-orbit coupling and the inversion symmetry breaking, the states near the Weyl node are spin-polarized with spin-texture highly correlated to the chirality of the Weyl node. It leads to unusual nonlinear optical responses of Weyl semimetals, such as strong second harmonic generation and photogalvanic effect, as recently found in TaAs and CoSi. These discoveries offer new opportunities for a variety of applications, such as high-sensitivity terahertz photodetector and high-frequency microwave rectification. With a single Weyl node near the Fermi level, CoSi serves as an ideal platform to study nonlinear optical properties associated with the Berry curvature near the node. Here we aim to reveal the second-order optical susceptibility related to the interband electronic transition across a single Weyl cone. We applied a broadband heterodyne-detected sum-frequency-generation spectroscopy to characterize CoSi crystals with an incoming photon energy of 0.2 –1 eV, corresponding to electron transition across single or double Weyl cone(s). With polarization-dependent experiments, we separately determined the two independent complex elements in the nonlinear optical susceptibility tensor. Our quantitative analysis was executed and confirmed via SHG microscopic study through a crystal-orientational analysis on different domains of a multi-domain CoSi crystal. We shall present our spectrum interpretation with helps of a density functional calculation in the talk. |
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T00.00131: Probing the Type-II Dirac Semimetal Platinum Ditelluride(PtTe2) through Electronic Transport Measurements at Low Temperatures Anise E Mansour, Patrick T Barfield, Vinh Tran, Kenta Kodama, Archibald . Williams, Warren L Huey, Joshua E Goldberger, Claudia Ojeda-Aristizabal Platinum Ditelluride (PtTe2) is a member of a class of materials called Type II Dirac Semimetals (DSMs) that have low energy fermionic excitations governed by the Dirac equation. Most importantly, Dirac fermions in these materials are not constraint by the Lorentz invariance. In view of understanding the electronic properties of random Cr alloys of PtTe2 that are known to be air-stable layered ferromagnets, we present preliminary electronic transport measurements at low temperatures of thin PtTe2 crystals. |
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T00.00132: Thermal difference reflectivity of tilted 2D Dirac systems Miguel A Mojarro Ramirez, Ramón Carrillo Bastos, Jesús A Maytorena We investigate the thermal derivative spectra of the optical reflectivity from massive tilted Dirac systems. The density of states and temperature dependence of the chemical potential are obtained as previous steps to calculate the optical conductivity tensor at finite temperature through a thermal convolution. Changes in reflection caused by variations of temperature allow a sharp identification of critical frequencies of the optical response. These spectral features in the thermoderivative spectrum allow in turn the determination of energy gaps and tilting of the band structure. Comparison between the spectra of several low-energy Dirac Hamiltonians is presented. The results suggest that thermal difference spectroscopy might be a useful technique to probe interband transitions of 2D Dirac fermions. |
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T00.00133: Electronic properties of the type-II Dirac Semimetal PtTe2 probed through Angle Resolved Photoemission Spectroscopy (ARPES) Ivan Pelayo, Derek C Bergner, Warren L Huey, Archibald . Williams, Ziling Deng, Luca Moreschini, Jonathan D Denlinger, Wolfgang E Windl, Alessandra Lanzara, Joshua E Goldberger, Claudia Ojeda-Aristizabal A material’s crystal structure imparts constraints on the momentum and energy of the electrons in the crystal, forming an electronic band structure with potentially interesting topological properties. This is the case of PtTe2, a semimetal where band crossings lead to type-II bulk Dirac excitations, consequence of the violation of Lorentz invariance, and confirmed by previous ARPES studies. |
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T00.00134: Leaking Majorana bound state in a double T-shape quantum dot interferometer. Alejandro P Garrido, Pedro A Orellana, Juan P Ramos Andrade, David Zambrano We investigate the transport properties through a nanostructure formed by two quantum dots coupled to two normal contacts in an interferometer configuration. In turn, each quantum dot is coupled to a topological superconducting nanowire, hosting Majorana bound states at its ends. An external magnetic flux is considered across the area enclosed by the interferometer. We investigate the physical quantities of the system by means of the Green's function formalism. We find that the magnetic flux cover and uncover the projection of majorana bound states (MBS) and bound states in the continuum (BIC) on the linear conductance, suggesting that only switching this parameter we can manipulate both kind of bound states.This result suggest a novel device, allowing manipulation of quasi-particles that obey non-abelian statistic, that are exceptional candidates for quantum computation implementations. |
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T00.00135: Emergent Topological Chiral Superconductivity in a Triangular-Lattice t-J Model Yixuan Huang, Shou-Shu Gong, Donna Sheng Topological superconductivity (TSC) is a highly sought-after superconducting state hosting topological order and Majorana excitations. In this work, we explore the mechanism to the TSC in the doped Mott insulators with time-reversal symmetry (TRS). Through large-scale density matrix renormalization group study of an extended triangular-lattice t-J model on the 6- and 8-leg cylinders, we identify a d + id-wave chiral TSC phase with spontaneous TRS breaking, which is characterized by a Chern number C = 2 and quasi-long-range superconducting order. We map out the quantum phase diagram with tuning the next-nearest-neighbor (NNN) electron hopping and spin interaction. In the weaker NNN-coupling regime, a charge stripe phase coexisting with strong spin fluctuations and fluctuating superconductivity is revealed. The TSC emerges in the intermediate-coupling regime, which has a transition to a d-wave superconducting phase at larger NNN couplings. The emergence of the TSC is driven by geometrical frustrations and hole dynamics, which suppress spin correlation and charge order, leading to a topological quantum phase transition. |
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T00.00136: Engineering an axion insulator phase in superlattices without inversion symmetry RAJIBUL ISLAM, Sougata Mardanya, Alexander Lau, Giuseppe Cuono, Tay-Rong Chang, Mohammad Saeed Bahramy, Bahadur Singh, Carlo M. Canali, Tomasz Dietl, Carmine Autieri We study the interplay between magnetism and topology in three-dimensional HgTe/MnTe superlattices stacked along the (001) axis. Our results show the evolution of the magnetic topological phases with respect to the magnetic configurations. An axion insulator phase is observed for the antiferromagnetic order with out-of-plane magnetization direction below a critical thickness of MnTe, which is the ground state amongst all magnetic configurations. The axion insulator phase evolves into a trivial insulator as we increase the thickness of the magnetic layers. By switching the magnetization direction into the $ab$ plane, the system realizes different antiferromagnetic topological insulators depending on the thickness of MnTe. |
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T00.00137: Theoretical modeling of the formation of Skyrmions in Fe-Gd Alana Okullo, Sougata Mardanya, Joshua J Turner, Arun Bansil, Sugata Chowdhury Skyrmions are one of the most complex magnetic orders observed and consist of a localized excitation |
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T00.00138: Giant anomalous thermal Hall effect in tilted type-I magnetic Weyl semimetal Co3Sn2S2 Abhirup Roy Karmakar, Snehasish Nandy, Arghya Taraphder, Gour Prasad Das The recent discovery of magnetic Weyl semimetal Co3Sn2S2 opens up new avenues for research into the interactions between topological orders, magnetism, and electronic correlations. Motivated by the observations of large anomalous Hall effect due to large Berry curvature, we investigate another Berry curvature-induced phenomenon, the anomalous thermal Hall effect in Co3Sn2S2. We study it with and without strain, using a tight-binding Hamiltonian derived from first principles density functional theory calculations. We first identify this material as a tilted type-I Weyl semimetal based on the band structure calculation. Within the quasi-classical framework of Boltzmann transport theory, a giant anomalous thermal Hall signal appears due to the presence of large Berry curvature. Surprisingly, the thermal Hall current changes and even undergoes a sign-reversal upon varying the chemical potential. Furthermore, applying about 13 GPa stress, an enhancement as large as 33% in the conductivity is observed; however, the material turns into a non-tilted Weyl semimetal. In addition, we have confirmed the validity of the Wiedemann-Franz law in this system for anomalous transports. We propose specific observable signatures that can be directly tested in experiments. |
Author not Attending |
T00.00139: Tuning of quantum anomalous hall conductivity using different stacking of TI/FM heterostructure in room temperature Surasree Sadhukhan The coupling between topology and magnetism can boost the rich fundamental physics |
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T00.00140: Mapping out the topological phase diagram of FeSn Soumya Sankar, RUIZI LIU, Chengping ZHANG, Qifang Li, KUN QIAN, Jiangchang Zheng, Caiyun Chen, Zi Yang Meng, Kam Tuen Law, QIMING SHAO, Berthold Jaeck Metallic kagome magnets exhibit a flat band and a Dirac point in their electronic structure and long-range magnetic order. The combination of these properties creates favorable conditions to search for strongly correlated and topological electronic states. The near-ideal kagome band structure of the intermetallic kagome series X1Y1 offers opportunities to investigate the interplay between strong electronic correlations, topology, and magnetism. |
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T00.00141: Ultrafast dynamics in the Sb doped MnBi2Te4 magnetic topological insulator Chi-Chen Tsai, Jiunn-Yuan Lin, Chih-Wei Luo, Nidhi Puri, Wen-Yen Tzeng, Jiun-Haw Chu, Cheng-Chien Chen MnBi2Te4 is recently identified as an intrinsic antiferromagnetic (AFM) topological insulator which is considered as a suitable material for the study of novel topological quantum phenomena whose possible behavior and ultrafast dynamics could be investigated through a versatile femtosecond time-resolved spectroscopy under applied magnetic field and temperature. In this work, topological quantum phase transition is studied in the magnetic topological insulator, MnBi2-xSbxTe4 (x=0.19), which is MnBi2Te4 mixed with antimony. It focusses on the phase transition induced by chemical substitution, magnetic field, and ultrafast lasers. The optical pump-probe (OP-OP) measurements are performed in the magneto-optical closed-cycle cryostat (Opti-Cool) to reveal and study the ultrafast dynamics about MnBi2-xSbxTe4 (x=0.19) at room temperature and low temperature (2 K). A continuously increasing magnetic field upto 7 T is also applied during the low temperature condition to observe the changing ultrafast dynamics crossing the spin-flop situation. In addition, we also plan to perform the Superconducting Quantum Interference Device (SQUID) to confirm the magnetic moment of anti-ferromagnetic (AFM) state at Neel temperature and magnetic level for the origin of spin-flop situation. |
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T00.00142: Pressure tuning of the Berry phase in BaMnSb2 Hong Xiao The Sb square net in BaMnSb2 is reported to host nearly massless Dirac fermions. At ambient pressure, BaMnSb2 shows strong Shubnikov-de Haas (SdH) oscillations with a pi Berry phase. In this work, we study BaMnSb2 under different pressures. It is found that the frequency of the SdH oscillation remians almost unchanged, hence the cross-section area of the Fermi surface does not change much with pressure. Notably, there is a sudden change in the phase factor of the oscillations around a critical pressure of P = 2.5 GPa, which suggests a possible topological phase transition in BaMnSb2. |
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T00.00143: Molecular beam epitaxy growth and Scanning Tunneling Microscope study of FeSn-type kagome metals Jiangchang Zheng, Berthold Jaeck, Caiyun Chen, Soumya Sankar, Yihsin Lin The two-dimensional kagome lattice combines a flat band and a Dirac point in its electronic structure which could give rise to strongly correlated and topological electronic states. The FeSn-type compounds in which transition metal atoms form a layered lattice structure have recently emerged as a model kagome system. Owing to the reduced interlayer coupling between the individual kagome planes, the near ideal kagome electronic states provide a rich platform to explore the interplay of topology, magnetism, and strong electronic correlations. |
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T00.00144: Spectroscopic characterization of 2D van der Waals antiferromagnetic topological insulators MnBi2Te4(Bi2Te3)n Jacob Hanson-Flores, Gregory Fritjofson The recent discovery of 2D van der Walls (vdW) magnetic topological insulators (TIs) has opened new avenues towards spintronics research from combining unique electronic properties arising from nontrivial band structures and the magnetic degree of freedom when magnetic ordering also establishes in the same material. MnBi2Te4(Bi2Te3)n represents an excellent example of this, being identified as a vdW TI with antiferromagnetic ordering for n=0,1,2. While emphasis has been placed into studying its electronic and magnetic properties using techniques like ARPES, transport, and magnetometry, little spectroscopic characterization has been reported to date. In this study we perform a series of low frequency measurements at varied temperatures and magnetic fields strengths and orientations that show clear antiferromagnetic modes in compounds with n=1 and n=2. The motion of the antiferromagnetic modes with the direction of application of the magnetic field reveal the anisotropic nature of the system, characterized by an easy magnetic symmetry axis and a corrugated hard plane that change slightly with the stoichiometry variation. Our results show how the transition temperature also varies between n=1 and n=2 compounds, indicating that the exchange interaction originating the antiferromagnetic order changes with the interlayer configuration. |
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T00.00145: Observation of flat bands in niobium halide semiconductor Alexis J Agosto-Cuevas, Sabin Regmi, Tharindu Warnakulasooriya Fernando, Yuzhou Zhao, Anup Pradhan Sakhya, Gyanendra Dhakal, Iftakhar Bin Elius, Hector Vazquez, Jonathan D Denlinger, Jihui Yang, Jiun-Haw Chu, Xiaodong Xu, Ting Cao, Madhab Neupane Kagome materials are potential systems for Dirac fermions and flat bands, which make them suitable grounds for the study of topology and electronic correlations in geometrically frustrated quantum materials. This study investigates the electronic structure of one such material, a niobium halide semiconductor, with a breathing kagome lattice of niobium atoms. We reveal the presence of multiple flat and weak dispersing bands, that are well captured in theoretical band calculations as well. Being a layered van der Waals material with a magnetic monolayer, this system will open up avenues toward the study of electronic correlations, magnetic order, and their interplay in two dimensions as well as toward its potential applications. |
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T00.00146: Vibronic excitations in resonant inelastic x-ray scattering spectra of K2RuCl6 Naoya Iwahara, Shouta Shikano, Vieru Veacheslav The interplay of the strong spin-orbit coupling and superexchange interaction could make the cubic compounds with nonmagnetic d4 ions magnetic [1]. |
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T00.00147: The collective modes of the charge density wave (CDW) in (TaSe4)2I studied with time-resolved x-ray scattering Ryan A Duncan, Quynh L Nguyen, Gal Orenstein, Gilberto De La Pena, Viktor Krapivin, Yijing Huang, Chance Ornelas-Skarin, Soyeun Kim, Simon L Bettler, Oscar Qu, Peter Abbamonte, Daniel P Shoemaker, Samuel W Teitelbaum, Fahad Mahmood, David A Reis, Mariano Trigo (TaSe4)2I (TSI) is a quasi-1D charge-density-wave (CDW) material and Weyl semimetal that has attracted much recent interest due to recent claims of the experimental observation of an axionic insulator phase. We studied the CDW collective modes of TSI using time-resolved x-ray scattering at the LCLS and SACLA free electron laser (FEL) facilities. We observe sub-THz oscillations at the CDW sidebands, and assign a component at 0.11 THz as an amplitude mode of the CDW. We analyze the amplitude mode signal with a coupled-mode Ginzburg-Landau model and find excellent agreement with experiment. In addition to the amplitude mode signal we also observe low-frequency dispersive signal components in the vicinity of the CDW sidebands, which we interpret as signals arising from photoexcited CDW phase modes. |
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T00.00148: Phase Diagram for Light-Induced Superconductivity in κ-(ET)2-X Sebastian Fava, Michele Buzzi, Daniele Nicoletti, Gregor Jotzu, Kazuya Miyagawa, Kazushi Kanoda, Alyssa M Henderson, Theo Siegrist, John A Schlueter, Moon-Sun Nam, Arzhang Ardavan, Andrea Cavalleri In high-Tc cuprates and alkali doped fullerides, driving of specific phonon modes with mid-infrared laser pulses has been shown to induce transient superconducting-like optical properties for temperatures far above the equilibrium Tc. Here, we discuss an analogous effect in the quasi two-dimensional organic superconductor κ-(ET)2Cu[N(CN)2]Br. At equilibrium, this material bears similarities to high-Tc cuprates, showing unconventional superconductivity that emerges from a correlated metallic state with a Tc of 11 K. In a series of non-equilibrium experiments, we resonantly excite local vibrational modes of the ET molecule and probe the transient conductivity of the material with THz spectroscopy. Starting from the equilibrium metallic state at T >> TC, we observe a photo-induced response compatible with that of a transient superconductor, which is strongly reduced when the pump wavelength is tuned away from vibrational resonances. When performing the experiment across the bandwidth tuned phase diagram of this family of compounds, this effect is observed only in κ-(ET)2Cu[N(CN)2]Br, indicating that proximity to the Mott insulating phase and possibly the presence of preexisting superconducting fluctuations are prerequisites for this effect. |
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T00.00149: Dynamics of light-induced self-intercalation in TaS2 Joshua S Lee Chemical intercalation in transition metal dichalogenides (TMDs) has long since attracted attention as an effective method of modifying the electronic landscape, the interactions between layers across the van-der-Waals gap, and even in electrochemical energy storage for battery technology. There have been recent advances in the fabrication of intercalated TMDs, including molecular-beam epitaxy and chemical vapor deposition methods. Here, we report a novel method of self-intercalation in 1T-TaS2 via application of near-infrared light pulses, with tunable tantalum concentration by varying exposure time as well as pulse energy. Using time-resolved electron diffraction, we further characterize the dynamics of the intercalated tantalum atoms, in comparison to that of the host lattice, after pulsed photoexcitation. We also report a reversible phase transition in which the diffraction peaks associated with the tantalum intercalates disappear and reappear near a critical temperature, corresponding to a transition analogous to sublimation. Our results may provide effective avenues for intercalation of other TMDs, an important area of interest for battery technology. |
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T00.00150: Impulsive Light-driven CDW wavevector modulation in 1T-TiSe2 Samuel W Teitelbaum, Mariano Trigo, David A Reis, Gilberto De La Pena, Sefaattin Tongay, Antia S Botana, Robert A Kaindl, Hasan Yavas, Takahiro Sato, Larissa Boie, Matthew Hurley, Viktor Krapivin, Alex H Miller, Priyadarshini Bhattacharyya, Steven L Johnson, Vladimir Ovuka, Yijing Huang, Gal Orenstein 1-T titanium diseleinde (1T-TiSe2) has been the subject of much study due to its prototypical second-order commensurate charge density wave (CDW) transition. The CDW phase competes with superconductivity, which is also typical of a large family of transition metal dichalcogenides. Below the CDW transition temperature, a soft TA phonon at the L point (q = [ ½ ½ ½]) condenses into long-range order. This phase transition was recently shown to have strong excitonic character with characteristics of an excitonic insulator, leaving open questions about the role of electron-phonon coupling in the CDW transition. To investigate this electron-phonon coupling, we performed optical pump, hard x-ray probe experiments on TiSe2 at LCLS to perturb the electronic states and observe the impulsive structural response of the material far from equilibrium. We observe coherent oscillations in the scattered x-ray intensity as a function of time near the CDW wavevector of 1T-TiSe2 upon optical excitation, which we interpret as a time-dependent modulation of the CDW wavevector based on the wavevector-dependent amplitude and phase of the coherences. |
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T00.00151: Ultrathin crystals of bismuth grown inside atomically-smooth van der Waals materials Laisi Chen, Amy X Wu, Naol Tulu, Joshua Wang, Adrian Juanson, Kenji Watanabe, Takashi Taniguchi, Yinong Zhou, Chaitanya A Gadre, Marshall A Campbell, Luis A Jauregui, Xiaoqing Pan, Ruqian Wu, Javier Sanchez-Yamagishi Confining materials to two-dimensional forms changes the behavior of electrons and enables new devices. However, most materials are challenging to produce as uniform thin crystals. We present a new synthesis approach where crystals are grown in a nanoscale mold defined by atomically-flat van der Waals (vdW) materials. By heating and compressing bismuth in a vdW mold made of hexagonal boron nitride, we produce ultrathin crystals less than 10 nanometers thick with flat surfaces. Cryogenic measurements of the ultrathin bismuth demonstrate high quality electronic transport exhibiting quantum oscillations and a 10x larger residual resistance ratio compared to thin films grown by molecular beam epitaxy. Our vdW-molded growth technique enables intrinsic transport studies of ultrathin bismuth, and also holds promise to achieve two-dimensional bismuth, a large-gap 2D topological insulator. Moreover, this approach provides a general way to synthesize ultrathin forms of non-vdW materials that are directly integrated into a vdW heterostructure. |
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T00.00152: Collective excitation of edge-modified graphene nanoribbons Thi-Nga Do, Po-Hsin Shih, Godfrey Gumbs, Danhong Huang We explored the collective excitation of graphene nanoribbon (GNR) under the influence of edge-modification. The theoretical framework was based on the tight-binding model in conjunction with the dielectric function. We observed unusual plasmon modes associated with collective excitation of the flat bands. Interestingly, these modes are analogous to magnetoplasmons of Landau-quantized electrons. This work provides a unique way to engineer discrete magnetoplasmon-like modes of GNRs in the absence of magnetic field. |
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T00.00153: Reliability of metallic contact properties of 2D semiconductors Hoseong Shin, Kwangro Lee, Sungwon Lee, Won Jong Yoo Electrical performances of semiconductor devices fabricated with 2-dimensional (2D) channel materials such as transition metal dichalcogenides (TMDCs) are strongly affected by the metallic contact interfacing with a 2D material. There have been various researches to investigate the interface formed between metals and 2D materials, by revealing typical figures of merit of contact properties which are contact resistance, Fermi level pinning, and Schottky barrier height (SBH). We find that the data of these contact properties obtained from 2D devices show large standard deviation, requiring to assess reliability of the contact properties of 2D semiconductors. In this study, we conducted experimental studies on how to get the reliable Schottky barrier heights (SBHs) formed at the interface of a metal (Ti) and a 2D material (MoS2). Here, we performed annealing for the purpose of decreasing contact resistance and investigating temperature dependent electrical behaviors of devices of various 2D thicknesses and channel lengths, together with the SBH analysis. By conducting this research, we can provide a practical guideline to obtain highly reliable contact properties of 2D semiconductor devices. |
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T00.00154: Characterizing the Electronic Properties of CuPc/Gr/hBN Heterostructures Vinh Tran, Francisco Ramirez, Jacob Weber, Ryan T Mizukami, Maya H Martinez, Patrick T Barfield, Kenji Watanabe, Takashi Taniguchi, Thomas Gredig, Claudia Ojeda-Aristizabal Copper Phthalocyanine (CuPc) is an molecular organic semiconductor with a non-zero magnetic moment. By depositing CuPc on a graphene/hBN electronic device, we find that the electronic properties of the original graphene/hBN heterostructure are significantly modified, revealed by a sign reversal of the magnetoresistance as well as the onset of an anisotropy in magnetic field. Differential conductance measurements show features that change with temperature, pointing to a rearrangement of the CuPc molecules on the graphene/hBN surface as the temperature is increased. Atomic Force Microscopy (AFM) show a different molecular arrangement of the CuPc molecules on graphene/h-BN with respect to hBN. |
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T00.00155: Analytical study of morphology-related defects in epitaxial graphene for high-performance application Ching-Chen Yeh, Yanfei Yang, Linli Meng, Alireza R Panna, Tehseen Adel, Angela R Hight Walker, Dean G Jarrett, David B Newell, Albert F Rigosi, Randolph E Elmquist, Chi-Te Liang Large-scale of homogeneous high-quality graphene can be achieved by epitaxial growth on a silicon carbide substrate [1], offering a promising opportunity for commercialization of graphene-based devices including the quantum Hall resistance standard [2], highly sensitive photodetectors [3], Hall effect sensors [4] etc. |
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T00.00156: Elastic properties of graphite moiré patterns using STM tip-induced deformation Nirjhar Sarkar, Prabhakar R Bandaru, Robert C Dynes Highly Oriented pyrolytic graphite (HoPG) is the only monoatomic crystal found to host naturally formed moiré patterns on its cleaved exfoliated surfaces which are coherent over micrometers with fixed periodicities. This is in contrast to twisted graphene layers where the moire pattern is under considerable strain and doesn't show the same long range coherence. In this work, we use STM tip-induced deformation to externally strain moiré patterns in Graphite and observe how they respond mechanically. This reveals the crystal orientation dependent elastic properties as a function of twist angles. We observe lateral stretching of domain walls (DWs) in graphite moiré which are unseen in graphene moiré. Surface deformation of formed graphitic Moiré patterns reveals the inter-layer van der Waals (vdW) strength varies across its domains. |
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T00.00157: Nonreciprocal and nonlinear charge transport effect in dual-gated bilayer graphene Cho-Hao Lu, Cheng-Tung Cheng, Liang Li, Wei-Li Lee, Wu-Jing Chen The search for single-phased material systems that show large nonreciprocal and nonlinear charge transport effect (NRTE) has attracted many attentions recently, which may lead to promising electronic applications. Here, we demonstrated such a NRTE in a dual-gated bilayer graphene (BLG) system without requiring external magnetic field. Owing to the unique pseudospin (or valley) degree of freedom in gapped chiral fermions with trigonal warping, the displacement field applied on a BLG not only breaks the inversion symmetry but also effectively removes the cancellation of NRTE from two different valleys, and it results in a large NRTE signal that grows with the excitation current and displacement field strength. The demonstration of full electric-field tuning of the nonreciprocal transport effect without magnetic field may provide an alternative route for valleytronics using two-dimensional based devices. |
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T00.00158: Tunability of Thermal Conductivity in 2D-Covalent Organic Frameworks Emma Tiernan, Zoheb Hirani, John Tomko, Lidia Kuo, Nathan Bradshaw, Nicholas Williams, David Burke, Austin Evans, Mark C Hersam, Patrick Hopkins, William Dichtel Covalent organic frameworks (COFs) are a unique class of material, in which chemists can easily modulate multiple properties of the COFs by varying the nodes and linkers that make up the framework. The interchangeability of these organic building blocks allows for the structures to potentially have a multitude of applications but were limited due to the COFs polycrystalline powder form. In recent years, there has been a large effort to grow 2D COF thin films, which resulted in films with thermal conductivities of 1.0 W m-1 K-1. In this presentation, we will use both time-domain thermoreflectance (TDTR) and steady state thermoreflectance (SSTR) to measure thermal properties of boronate-ester and imine-linked 2D COF thin films. TDTR and SSTR are non-contact, laser-based, pump-probe measurement techniques, which relate the change in reflectivity of the sample surface, to the thermal conductivities of the COF films below. We will discuss the effects of film thickness, connectivity, and pore functionality on the thermal properties of COF thin films. |
Author not Attending |
T00.00159: Photoluminescence Investigation of Nano-flakes of MnPS3 Antiferromagnet Vigneshwaran Chandrasekaran, Tai C Trinh, Xiangzhi Li, Suryakant Mishra, Huan Zhao, Andrew Jones, Han Htoon Transition metal thiophosphates MPS3 (M=Mn, Fe, Ni) are considered as promising platform for investigating novel magneto-optical phenomena for applications in spintronics. In particular, MnPS3 is interesting because the photoluminescence (PL) from micrometer-sized exfoliated flakes was reported to have strong interaction with the Néel ordered state (TN = 78K) that persists down to monolayer thickness allowing to tune the optical properties by forming different heterostructures. Here we investigate the optical properties of crystalline nanometer-sized flakes of MnPS3. AFM characterization shows thickness of the flakes ranging from few to tens of nm and the lateral size about tens of nm. In contrast to PL emission from micrometer-sized flakes which were reported to have broader linewidth around 100nm [1], we observe sharp emission peaks for nano-flakes with the linewidth lesser than 2 nm. We also observe the emission peaks varies from one nano-flake to another ranging from 575nm to 630 nm whereas the micro-flakes have fixed peaks at 566 nm and 941 nm. In addition, our nano-flakes also exhibit strong degree of linear polarization, blinking and spectral diffusion characteristics. |
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T00.00160: Metavalent Bonding Origins of Unusual Properties of Group IV Chalcogenides Raagya Arora, Umesh V Waghmare, C. N. R. Rao A distinct type of metavalent bonding (MVB) was recently proposed to explain unusual set of anomalous functional properties of group IV chalcogenide crystals. However, electronic mechanisms of MVB and emergent properties are yet to be understood. Through theoretical analysis of evolution of MVB along continuous paths in structural and chemical composition space, we show that MVB arises in rocksalt chalcogenides stabilized as weakly broken symmetry states of the parent metal of simple cubic crystal of Group V metalloid. Symmetry-breaking structural and chemical polar fields couple with its degenerate frontier states opening up a gap resulting in MVB state with high polarizability and sensitivity to bond-lengths. It transforms discontinuously to covalent and ionic semiconducting states with stronger symmetry breaking structural and chemical fields respectively. Wannier function analysis reveals mixed, long-range bonding and antibonding pp, sp orbital interactions, supporting high coordination numbers. MVB involves bonding and antibonding pairwise interactions alternating along linear chains of at least five atoms, which facilitate long range electron transfer in response to polar fields causing unusual properties. Our precise picture of MVB predicts anomalous second order Raman scattering as an addition to set of their unusual finger-printing properties, and will guide in design of new metavalent materials with improved thermoelectric, ferroelectric and nontrivial electronic topological properties. |
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T00.00161: Creating periodic vacancies in atomic chains within the individual layers of a 2D magnet Eugene Park, Mads A Weile, Julian P Klein, John P Philbin, Zdeněk Sofer, Prineha Narang, Frances M Ross Van der Waals 2D magnetic materials have emerged as a novel platform that offers unique optoelectronic, magnetic, and quantum properties.1 Such low-dimensional spin systems have vast potential in applications such as spintronics and nanoscale magnetic devices. Therefore, the ability to engineer the structure and defects with respect to magnetic, optical, and electronic properties is critical. |
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T00.00162: Raman spectroscopy and MCD of magnetic moiré superlattices formed by twisted double bilayer CrI3 Gaihua Ye, Zhipeng Ye, Haiwen Ge, Rui He, Hongchao Xie, Xiangpeng Luo, Kai Sun, Liuyan Zhao We fabricate twisted double bilayers (tDB) of a 2D magnet, chromium triiodide (CrI3), and demonstrate the successful twist engineering of 2D magnetism in them. We identify Raman signatures of a new magnetic ground state that is distinct from those in natural two-layer (2L) and four-layer (4L) CrI3. We show that for a very small twist angle, this emergent magnetism can be well approximated by a weighted linear superposition of those of 2L and 4L CrI3, whereas for a large twist angle, it mostly resembles that of isolated 2L CrI3. However, at an intermediate twist angle, there is a finite net magnetization that emerges because spin frustrations are introduced by competition between ferromagnetic and antiferromagnetic exchange coupling within individual moiré supercells. Magnetic circular dichroism (MCD) spectroscopy measurements reveal the evidence of noncollinear spin texture in tDB CrI3. Our results establish the emergence of noncollinear spins from magnetic moiré superlattices and provide a versatile platform to explore nontrivial magnetism with noncollinear spins. |
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T00.00163: Nonlinear optics in ferrofluid-based hyperbolic metamaterials Nathaniel B Christopher, Jonathon Cartelli, Benjamin Kist, Johnathan Perry, Stephanie Spickard, Mary S Devadas, Vera Smolyaninova, Igor Smolyaninov Hyperbolic metamaterials allow for a plethora of non-traditional methods of manipulating light. In this work we implement theoretical proposal of Smolyaninov and Narimanov (Phys. Rev. Lett. 105, 067402 (2010)) who demonstrated that extraordinary light waves in hyperbolic metamaterials may exhibit “two times” physics behavior. This behavior is observed via experimental study of nonlinear optics of iron/cobalt ferrofluid-based hyperbolic metamaterial, which shows considerable similarities with gravitation theory. We will present high-resolution images of self-focusing effect in this metamaterial, which were obtained as a function of light intensity. Appearance of self-focused filaments analogous to self-gravitating bodies was observed. The dynamics of this filaments resembling gravitational attraction will be discussed. |
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T00.00164: Characterization of Pt quantum dots fabricated by electron-beam induced deposition Binod D.C., Noah Austin-Bingamon, Yoichi Miyahara |
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T00.00165: Metasurface engineering of transition metal dichalcogenides by anisotropic etching Dorte R Danielsen, Anton Lyksborg-Andersen, Kirstine E Sandager Nielsen, Bjarke S Jessen, Timothy J Booth, Manh-ha Doan, Yingqiu Zhou, Avishek Sarbajna, Søren Raza, Lene Gammelgaard, Peter Bøggild A major objective within two-dimensional materials research is to tailor the electronic and photonic properties via nanopatterning. Electron beam lithography is a flexible technique that is widely used to pattern large areas with regular nanostructures. However, nanometer-scale edge roughness and resolution variability typically compromise the pattern quality. |
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T00.00166: Plasmonic angstrom-scale gap-dependent enhancement with gold nanosphere metasurfaces. Joseph B Herzog, Stephen J Bauman, Ahmad A Darweesh, Miles Furr, Meredith Magee, Christos Argyropoulos This work reports experimental and computational results of gap–dependent surface-enhanced Raman Spectroscopy (SERS) for nanogaps that vary between 4 - 30 angstroms of two different analytes, trans-1,2-bis(4-pyridyl)-ethylene (BPE) and benzenethiol (BZT), pushing the boundary of previous SERS gap size limits. Raman spectroscopy is a valuable, highly sensitive detection tool, and SERS can improve the sensitivity even further. The substrates used in this work are plasmonic metasurfaces with a single layer of a hexagonally close packed gold nanospheres with a ligand surface that sets the nanoscale interparticle gap. The plasmonically enhanced Raman signal increased as the gap-size decreased, as expected, confirmed, and predicted by computational electromagnetic models; though, there was enhancement quenching that was measured for gap sizes below 1 nm. Therefore, in addition to using a "local" computational model, a quantum "nonlocal" model was used to account for electron tunneling effects, which can explain the plasmonic enhancement quenching that was observed for the sub 1 nm gap sizes. This work adds to the growing field of angstrom-scale optics, suggesting that in this range, plasmonic models would require a nonlocal/quantum model to accurately predict optical enhancement. |
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T00.00167: Photoluminescence enhancement of perovskites nanocomposites using ion implanted silver nanoparticles Shahid Iqbal Metal-enhanced photoluminescence by 70 keV Ag ions implanted at various fluences in quartz substrates was studied using drop casted CsPbX (X = Br3, I3, BrI2) perovskites. The concentration and depth profile of the implanted Ag were determined by Rutherford Backscattering Spectrometry. Ag nanoparticle’s existence was confirmed by optical absorption spectroscopy. Photoluminescence enhancement was obtained using steady-state photoluminescence spectroscopy and enhancement was observed for CsPbBrI2 and CsPbI3 reaching as high as 3.6 and 5.9-fold, respectively. Whereas, a 60% photoluminescence quenching was observed for CsPbBr3, which could be attributed to the non-radiative energy transfer from perovskite to nanoparticles. |
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T00.00168: Characterization of Lightsail Light-Matter Interaction and Nonlinear Dynamics by Microscopic Common-Path Vibrometry Lior Michaeli, Ramon Gao, Michael D Kelzenberg, Claudio U Hail, Harry Atwater Dynamic control of macroscopic objects with light has recently became a flourishing research front, largely catalyzed by the ambitious goal of the Breakthrough Starshot Initiative to launch laser-driven lightsails for space exploration. However, for a high-intensity optical drive the heat generated in the lightsail will inevitably affect its dynamics. We have developed a method based on a microscopic common path vibrometer to perform sensitive optical measurements and characterize the light-matter interaction and heat-induced nonlinearity of lightsails. We report the observation of rich nonlinear dynamics in optically pumped tethered silicon nitride lightsails. These include high-order parametric instabilities, injection locking, frequency-mixing and hysteresis induced by Duffing nonlinearity. We find that the spectral positions of the parametric instability tongues deviate from the expected subharmonic <!--[if gte msEquation 12]> style='mso-bidi-font-style:normal'>2 style='font-size:12.0pt;mso-ansi-font-size:12.0pt;mso-bidi-font-size:12.0pt; |
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T00.00169: Unconventional electromagnetic surface waves at the interface of two metals Daryna Soloviova, David Schaefer, Vera Smolyaninova, Igor Smolyaninov It is well known that electromagnetic waves do not penetrate metal beyond the skin depth. Recently, it was theoretically predicted that in the presence of a gradual interface of two metals, the electromagnetic surface wave would experience low loss propagation along the diffuse boundary. In this configuration, the surface wave is predicted to propagate along such boundaries hundreds of times further than the skin depth. In this study, we have experimentally confirmed this prediction for the case of gold/silver diffused boundary. Overlap of gold and silver thin films was created, and propagation of the visible light was detected along the boundary. This result may enable extension of plasmonics into the UV range and enable novel approaches to silicon photonics. |
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T00.00170: Structure and Optical Property Prediction of Plasmonic Metasurfaces Fabricated by Shadow Sphere Lithography Yiping Zhao, Yanfeng Wang, Dexian Ye, Fengtong Zhao, Zhengjun Zhang Shadow sphere lithography (SSL) is a powerful nanofabrication method to produce various two-dimensional metasurfaces and three-dimensional metamaterials. However, one of the biggest challenges for SSL is that the physical properties of the fabricated nanostructures are very hard to accurately predict even the shapes of the structures can be modeled by the geometric shadowing effect. A Monte-Carlo (MC) simulation is developed to show that a dynamic shadowing effect due to the accumulation of materials on nanosphere monolayer template as well as the detailed thin film growth mechanism play key roles in determining the structural details. For one-to-three step based SSL fabrication, the nanostructures predicted by MC matches very well with those produced experimentally and the plasmonic properties predicted by these MC simulated structures are also consistent with the features obtained experimentally both qualitative and semi-quantitatively. This study indicates a possible solution to use MC simulation and numerical calculation to guide the design of the plasmonic metasurfaces and metamaterials based on SSL fabrication. |
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T00.00171: Atomistic investigation of phonon transport through nanoparticles Theodore Maranets, Yan Wang Phonon conduction across solid-solid interfaces has been commonly estimated via the acoustic mismatch model (AMM) and the diffuse mismatch model (DMM) in several forms. These theories are mainly applied to planar interfaces and are well understood, however, an accurate description of phonon scattering by non-planar interfaces has yet to be found. This subject is of particular interest for improvement of embedded nanoparticle composites that have demonstrated a great potential as low-cost but high figure-of-merit thermoelectric materials. Specifically, a nanoparticle can be viewed as a combination of two non-planar interfaces that, in addition to reflection and transmission, can induce phonon wave trapping, localization, and lagged dissipation effects. In this work, we apply atomistic phonon wave-packet simulations to uncover these effects with wavevector and mode dependence. We found two unreported phenomena: (1) phonon lensing and (2) phonon localization. Regarding (1), we found that spherical interfaces focus a uniform phonon wavefront similar to optical lenses focusing light. However, the spherical aberration of the phonon wave is much more diffuse, suggesting significant interference effects. Furthermore, localization of phonon energy (2) inside the NP is observed and is strongest when (1) is most prominent, suggesting a unique geometric interference phenomenon that affects both phonon wave dynamics and energy propagation. |
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T00.00172: Investigation of Confined and Interface Phonons in Acoustically Mismatched Heterostructures using Brillouin – Mandelstam Light Scattering Spectroscopy Dylan Wright, Erick A Guzman, Fariborz Kargar, Alexander A Balandin, Zahra Ebrahimnataj We report on the development of the advanced Brillouin – Mandelstam spectrometer tool and its use for the investigation of the confined and interface phonons in the acoustically mismatched heterostructures [1]. We studied the acoustically soft PMMA layers deposited on the acoustically hard single-crystal diamond substrate. The acoustic impedance is defined as a product of the mass density and sound velocity. Diamond and PMMA have a large acoustic impedance mismatch, allowing for the observation of confined and interface phonons. We observed evenly spaced peaks in the spectral range between the acoustic phonon peaks of diamond and the acoustic phonon peaks of PMMA layers suggesting the appearance of many confined polarization branches. We discuss the dependence of the observed phonon spectra on the thickness of the PMMA layer and the quality of the interface. The obtained results have implications for thermal transport across dissimilar interfaces. Diamond has been investigated for applications in electronics as a thermal management substrate and a wide-band-gap semiconductor channel. The knowledge of the phonon spectra of the diamond-based heterointerfaces is important for both types of applications. |
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T00.00173: First-principles study of the quasi-two-dimensional electron gas at LaInO3/BaSnO3 interfaces Minsik Oh, Se Young Park, min chul choi We investigate atomic and electronic properties of LaInO3/BaSnO3 (LIO/BSO) heterostructures using first-principles density functional theory and tight-binding modeling of the frontier orbitals. The charge transfer from the topmost layer of LIO to the interfacial BSO is observed as increasing the thickness of the LIO layers. The spatial distribution of the interfacial charge density profile as a function of LIO thickness is also investigated. The charge density profile as a function of the charge transfer is further investigated by a tight-binding model considering Hartree potential in which the model parameters, such as the effective mass of Sn-s bands and dielectric constants, are obtained by fitting the charge density profile from the first-principles calculations. Our results by solving the Poisson-Schrödinger equation with a thick BSO limit show that there is a significant change in the spatial extent of the interfacial electron gas with the degree of the charge transfer. We believe that our results provide the electronic structures and charge-density profiles by varying charge transfer in thick BSO limits, which could be useful for understanding the properties of the quasi-two-dimensional electron gas formed at the LIO/BSO interface. |
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T00.00174: Many-body description of shallow NV− centers in diamond: role of surface coupling on quantum sensors and qubits Arsineh Apelian Strongly correlated defect states found in negatively charged nitrogen-vacancy (NV−) centers offer an excellent platform for the control of individual excitations due to the defect's highly localized nature. This means the center's spatially localized bound states are well isolated from sources of decoherence, making it a leading candidate for quantum sensors and solid state qubit systems. To guarantee good sensing capabilities, engineering the defect as close as possible to the surface (a few nanometers in depth) is preferable. Nevertheless, shallow NV- centers are prone to decoherence due to the coupling to the surface impurities. In this work, we study sub-surface NV- centers in diamond using various surface types (100 and 111) and surface terminations (hydrogen and nitrogen terminators). Using density functional theory and many-body perturbation theory methods, we provide an accurate theoretical description for understanding various couplings and control mechanisms in these shallow NV- centers. We discuss the stability of the defect embedded into large slabs (up to 8 nm thickness) which constitute more than 13,000 electrons. Our results show the first realistic simulation of sub-surface NV- defects within the framework of stochastic many-body theory. |
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T00.00175: Electronic, magnetic, and quantum phenomena in doped boron nitride Hari Paudyal, Michael E Flatté, Durga Paudyal The substitutional doping of magnetic elements is one of the best techniques for developing tunable bandgaps and magnetism in layered materials with potential applications in future quantum technologies and memory devices. The interplay between local magnetic moments and electronic states in these materials is crucial, however in depth understanding of their properties and potential applications have been constrained due to a dearth of suitable candidates. Here, we present ab initio calculated electronic and magnetic properties along with quantum states generation with the help of magnetic dopants in wide bandgap insulators, such as transition metal doped boron nitride. Further, we examine their phonon frequencies for dynamical stability and explore their potential use in quantum information processing. |
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T00.00176: Compact quantum circuits of variational quantum eigensolver for quantum impurity models Rihito Sakurai, Wataru Mizukami, Hiroshi Shinaoka The dynamical mean-field theory (DMFT) is a local approximation theory where the entire system is divided into correlated atoms and an environment representing the rest of the system. The biggest bottleneck of DMFT calculations is solving a quantum impurity model consisting of correlated sites (orbitals) and non-interacting bath sites representing the environment. The impurity models typically include bath sites more than correlated orbitals by one order of magnitude. Solving this model takes exponential computational costs for classical computers. |
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T00.00177: Atomic-scale Fracture Modeling in Lithium disilicate Glass-Ceramics by Reactive Molecular Dynamics Simulations Sungwook Hong, Sung-yup Kim, Hyung Sub Sim Lithium disilicate (LS2) glass-ceramics have been successful in many industry applications such as display glasses, owing to their generally superior mechanical properties such as high flexural strength and fracture toughness. As such, it is vitally important to have fundamental understanding of mechanical characteristics of the glass ceramic materials to be extended to other commercial applications. However, effects of materials phase (e.g., the ratio of amorphous phase to crystal phase) on fracture mechanics still remain elusive. Here, we perform reactive molecular dynamics (RMD) simulations to reveal mechanical behaviors of LS2 glass-ceramics depending on volume fraction of crystal phases. We also identify key facture mechanisms of these materials which may help advance experimental design of higher quality glass-ceramic materials. We believe our work will make a unique contribution to the scalable and reliable synthesis of aerospace materials like glass-based composites at extreme conditions. |
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T00.00178: Phase Stability and Electric Polarization in High-Entropy Oxides for Electrocaloric Refrigeration Tara Karimzadeh Sabet, Simon Gelin, Ismaila Dabo The electrocaloric effect is of practical interest to the development of sustainable solid-state refrigeration technologies. High-entropy oxides [1] hold promise for electrocaloric cooling due to the intrinsic thermal stability of their polar phases. In this work, we study the phase stability and electrocaloric performance of the high-entropy perovskite (Na,Bi,Sr,Ba,Ca)TiO3. To enable the efficient sampling of the configurational space of (Na,Bi,Sr,Ba,Ca)TiO3, a novel approach is presented in which the Goldsmith tolerance factor of the perovskite structure is calculated along specific crystallographic directions. Preliminary studies suggest that this directional tolerance factor correlates to the mixing enthalpy of high-entropy perovskites and can reliably be used to predict thermodynamic formability. Upon further validation, this methodology may significantly reduce the computational cost and complexity of free-energy calculations in high-entropy perovskites and related crystal structures. |
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T00.00179: Machine learning-driven new material discovery Chanseok Kim, Mina Yoon, Jun Hee Lee The combination of physicochemical laws and empirical trial and error has long guided the design material. The space of hypothetical materials to be considered is incredibly large, and only a small fraction of possible compounds can ever be tested experimentally. The computational techniques of atomistic simulation and machine learning (ML) offer an avenue to rapidly invent new materials and navigate this enormous space. The recently proposed crystal graph convolutional neural network (CGCNN) offers a highly versatile and accurate machine learning (ML) framework by learning material properties directly from crystal graph representations. In this talk, we discuss the identification of high-quality candidates by CGCNN ML about physicochemical properties of delafossite and perovskite materials in various element combinations. For distinct material- and application-specific machine learning, we generated appropriate descriptors (the sets of parameters capturing the underlying mechanisms of a material's property) by benchmarking the sure independence screening and sparsifying operator (SISSO). |
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T00.00180: Competing Effect of Biquadratic and Heisenberg Coupling on Magnetic Tunnel Junction Molecular Spintronics Devices Pawan Tyagi, Andoniaina M Randriambololona, Christopher D'Angelo, Andrew Grizzle Heisenberg Exchange Coupling (HC) and Biquadratic Exchange Coupling (BQC) are present in magnetic tunnel junctions(MTJ) and nanoscale elements-based spintronics1. MTJ-based molecular spintronics (MTJMSD) offer an unprecedented new way to create devices and highly correlated physics phenomena. Molecular spin channels on the exposed edge of MTJ were found to produce strong exchange coupling experimentally and theoretically, and the nature of coupling was believed to be HC2. BQC – which leads to the perpendicular alignment of the spin vectors of the adjacent FM electrodes – also occurs via the insulator or molecular nanostructures. Little is known about the competing effects between these two types of interlayer exchange couplings on MTJMSDs. A systematic study was performed using Monte Carlo simulations (MCS) based on a 3D Heisenberg model. The BQC strength was varied for a device with no molecular HC as well as strong parallel and antiparallel molecular HC coupling. The physical and magnetic properties of the MTJMSD were examined. It was found that increasing BQC strength in an MTJMSD with strong parallel and antiparallel molecular HC had little effect on overall device magnetization as HC still ultimately dominated the device magnetization. The effect of BQC on the device’s magnetic equilibrium state was also examined through its temporal evolution. Results suggest that when only molecular BQC is present within the device, the device is unable to reach magnetic stability; on the other hand, when HC and BQC are present within the device, HC encourages the device to achieve greater stability. The results ultimately indicate BQC plays a lesser role in overall device magnetization dynamics as it cannot overcome the more substantial magnetization effect produced by the HC. The presence of BQC provides a plausible explanation for the experimentally observed difference in magnetic phase orientations other than parallel and antiparallel states around MTJMSD. |
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T00.00181: Topological structures in ferroelectric nanodots revealed from first-principles simulations Ellen Jannereth Ferroelectric materials are known to exhibit spontaneous polarization [1]. The behavior of bulk ferroelectrics is well understood. However, these materials exhibit unusual characteristics like topological vortices as their dimensionality decreases [2-4]. Using an effective Hamiltonian approach, we computationally investigate BaTiO3 (BTO) nanodots of various sizes ranging from 12nm to 40nm to study the vortex dipole patterns in 3D. The simulation is carried out at a temperature of 10K in the rhombohedral phase of BTO. Our analysis predicts the existence of multiple vortices in different cross-sections of the nanodot and the number of vortices present increases with dot size. The trajectory of the principal vortex in different cross sections is found to be along the diagonal of the dot. Furthermore, applying a DC electric field ranging from 0 to 2000kV/cm in steps of 200kV/cm annihilates the vortex at 1400kV/cm to introduce a homogenous pattern. Our findings offer new insights into low-dimensional ferroelectrics and can find potential applications in novel nanoelectronic devices. |
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T00.00182: Is light a source of degradation in perovskite solar cells? Junhyeok Bang Perovskite solar cells have attracted much attention as next-generation solar cells, and many studies are being conducted. However, one of the biggest issues in the perovskite solar cell is low stability or reliability. Several experiments have suggested that light is a source of degradation in perovskite solar cells, but the detail mechanism is yet to be understood. In this study, the light-induced degradation mechanism was analyzed based on the first-principles calculations. We found that the light-induced degradation of organic A-site molecules, which has been proposed in the previous experiments, is difficult to be occured. It was also found that light had little effect on the denaturation of perovskite materials. Through these results, a new degradation process of perovskite materials was proposed, and previous experiments were interpretated based on the process. |
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T00.00183: Electric Dzyaloshinskii-Moriya Interaction: its existence and electronic origin Peng Chen, Hongjian Zhao, Sergey Prosandeev, Sergey Artyukhin, Laurent Bellaiche The magnetic Dzyaloshinskii-Moriya Interaction (mDMI) revolutionized magnetism, since it is, e.g., at the heart of nontrivial non-collinear topological textures, such as vortices, skyrmions, and domain walls – that are fundamentally intriguing and technologically promising. Recently, experiments and numerical simulations have revealed the existence of topologically nontrivial electrical polar textures, that are the electrical counterparts of magnetic topological defects. Strikingly, their origins were typically assumed to be related to electrostatic boundary conditions rather than an intrinsic hypothetical electric analogous of the mDMI, that is an electric Dzyaloshinskii-Moriya Interaction (eDMI). In fact, such eDMI has long been assumed not to exist. In this poster, I will demonstrate the existence of eDMI. Moreover, I will show that (i) both eDMI and mDMI need electron hopping channels and local-inversion-symmetry breaking to occur; (ii) mDMI needs spin-orbit coupling (soc) to connect spin up and down, unlike eDMI; (iii) eDMI naturally exists in polar materials because of the general existence of local-inversion-symmetry breaking. Our results, therefore, suggest the existence of a new paradigm of noncollinear polar arrangements arising from intrinsic electric Dzyaloshinskii-Moriya Interaction. |
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T00.00184: Ferroelectric domain reconfiguration contributions to bulk photovoltaic effect in LuMnO3 Gervasi Herranz, Yunwei Sheng, Huan Tan, Ignasi Fina, Josep Fontcuberta Bulk photovoltaic effect (BPE), occurring in non-centrosymmetric materials, lead to a characteristic dependence of the short circuit photocurrent (JSC) and open circuit voltage (VOC), that oscillate when changing the light polarization. In ferroelectrics, the switchable nature of the polar domains implies that JSC and VOC may be dependent on the polarization direction. Therefore, BPE could constitute a tool to explore ferroelectric polarization switching dynamics. We shall report on the BPE measurements in ferroelectric hexagonal LuMnO3 single crystals and thin films. It will be shown the JSC oscillates in agreement with the crystal class symmetry of the compound. However, the amplitude of the measured oscillations is found to be largely affected by polarization back-switching occurring in presence on imprint or related electric fields. As a practical consequence, evaluation of the Glass tensor elements characterizing the BPE response and thus comparison to theoretical predictions is challenged. |
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T00.00185: Exchange bias and gate-tunable magnetic anisotropy in 2D multiferroic heterostructure Yinchang Ma Tuning the magnetism in the electronic approach is a goal that has been pursued in the field of spintronics for a long time. However, this goal is rarely achieved on 2D materials. Here, we realized the manipulation of magnetism by developing a novel 2D multiferroic heterostructure. The exchange bias was observed in anomalous Hall effect (AHE) measurement, showing the strong coupling between ferromagnetic order and antiferromagnetic order in the heterostructure. With the application of the back gate voltage, the hysteresis field reduced, as observed from the narrowed AHE loop, suggesting the effective manipulation on magnetic anisotropy. These findings indicate a new way to manipulate magnetism in 2D systems via magneto-electric coupling. |
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T00.00186: Linear high-field magnetoelectric coupling and ferroelectric order in a proposed Kitaev compound: Na2Co2TeO6: SHAMEEK MUKHERJEE We studied the ferroelectric (FE) order associated with a linear magnetoelectric coupling in kitaev compound Na2Co2TeO6. The ferroelectric order around ∼72 K (TFE), much above the antiferromagnetic ordering (TN) at 26 K, is confirmed by the pyroelectric and bias-electric field measurement. A reasonable value of the electrocaloric effect is observed around TFE. The magnetic entropy change (ΔSM) emerges at the onset of FE order, exhibits a maximum of around 35 K, which is also much higher than TN, pointing towards a dominant short-range ordering above TN. A structural transition is proposed to a polar P63 structure at TFE from a high-temperature P6322 space group, which accounts for the emergence of polar order. The distortion of the CoO6 octahedral and the layered honeycomb structure around TFE and TN has been discussed to correlate the significance of the magnetic frustration, the occurrence of FE order, the multi-caloric effect, and the feasible Kitaev spin liquid state. The multifunctional properties of the compound have drawn special attention and are of fundamental interest. |
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T00.00187: Temperature Dependance of Elastic Constants of K1-xLixTaO3 (KLT) Ferroelectric Relaxor Crystals using Resonant Ultrasound Spectroscopy Ashley Olson, Matthew P Yoder, Emily M Gima, Nathanael J Hillyer, Oleksiy Svitelskiy, Grace Yong, Lynn A Boatner Potassium Lithium Tantalum Oxide (KLT), although it is a very under-investigated material, represents a relatively simple model for relaxor ferroelectricity phenomenon. Moreover, it is optically transparent that makes it suitable for applications of adaptive optic devices. Temperature-dependent Resonant Ultrasound Spectroscopy (RUS) is a quick and nondestructive method to characterize elastic properties of materials, which makes it a useful for studying relaxor ferroelectrics. The sample is suspended between the excitation and receiving transducers. By transmitting and scanning the excitation frequencies, one can record a resonance spectrum of the sample to be able to determine a set of elastic constants of the sample through mathematical modelling. We report the results of our study of temperature dependence of the c11 elastic stiffness tensor constant for the KLT crystal with x=0.1 at a range of temperatures from 300K down to 65K. Anomalous softening of the c11 elastic constant reveal the critical temperature range of Tc at which the phase transition occurs. |
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T00.00188: Comparing ab initio methods to calculate polarization for high-throughput ferroelectric screening Abigail Poteshman, Francesco Ricci, Jeffrey B Neaton Ferroelectric materials exhibit spontaneous electric polarizations that can be tuned by external electric fields and have applications in information storage and electronic devices. While the polarization of a material can often be estimated using Born effective charges computed with density functional theory (DFT) and displacements relative to a nonpolar reference phase, prior high-throughput screening for candidate ferroelectric materials rely on the DFT-based Berry approach, accounting for the multivaluedness of the polarization by interpolating between the polar and nonpolar structures along a fictitious adiabatic path [1]. While this interpolation-based approach has identified new candidate ferroelectrics, it can fail to disambiguate branches or in cases where interpolated structures are spuriously metallic. Here, we compare these approaches with a recently proposed method, known as Berry flux diagonalization, which computes differences in Berry phase directly from the wavefunctions of polar and nonpolar structures, avoiding the calculation of the Berry phase polarization of multiple fictitious, interpolated structures [2]. Run times, accuracy, and limitations of these methods, with implications for high-throughput ferroelectric screening, will be discussed. |
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T00.00189: Toward liquid cell quantum sensing: Ytterbium complexes with ultra-narrow absorption Ashley Shin Chemical synthesis and design primarily occur in condensed phase environments, where concentration, solubility, temperature, and polarizability can be tuned to access specific reactivity and functionality. However, in quantum technologies (such as atomic vapor cells used in precision magnetometry), the energetic disorder induced by a fluctuating liquid environment acts in direct opposition to the precise control required for coherence-based sensing. Overcoming fluctuations requires a protected quantum subspace that only weakly interacts with the local environment. We report aferrocene-supported ytterbium complex ((thiolfan)YbCl(THF), thiolfan = 1,1′-bis(2,4-di-tert-butyl-6-thiomethylenephenoxy)ferrocene) that exhibits an extraordinarily narrow absorption linewidth in solution at room temperature with a full-width at half-maximum of 0.625 ± 0.006 meV. Detailed spectroscopic analysis allows us to assign all near infrared transitions to strongly atom-centered f-f transitions, protected from the solvent environment. A combination of density functional theory and multireference methods match experimental transition energies and oscillator strengths, illustrating the role of spin-orbit and asymmetric ligand field in enhancing absorption and pointing toward molecular design principles that create well-protected yet observable electronic transitions in lanthanide complexes. Narrow linewidths allow for a demonstration of extremely low-field magnetic circular dichroism at room temperature, employed to sense and image magnetic fields, down to Earth scale. |
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T00.00190: MAGNETISM
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T00.00191: Epitaxial Growth of Artificial Compounds based on Superlattices of Heusler Alloys Ethan I Fenwick, Frank Tsui Epitaxial growth of films and heterostructures containing two ternary Heusler alloys has been investigated with the film lattice and elemental composition along the growth direction artificially sequenced one atomic layer (AL) at a time. Non-equilibrium synthesis and properties of (111) films with different elemental sequences but the same average composition have been examined, e.g., lattices with a unit cell of 12 AL along 111 (8 AL of Co2MnSi and 4 AL of Fe2MnSi) and the various permutations of AL sequences, including Mn-Co-Si-Co-Mn-Co-Si-Co-Mn-Fe-Si-Fe (L21 stacking), Mn-Co-Co-Si-Mn-Co-Co-Si-Mn-Fe-Fe-Si (“inverse” Heusler stacking), and Mn-Co-Si-Co-Mn-Fe-Si-Co-Mn-Co-Si-Fe. Ge and SiGe alloys grown on Ge (111) substrates were used as the growth template to fine-tune the lattice mismatch with the films. The sequential AL deposition was controlled in realtime by atomic absorption spectroscopy and stepper-motor controlled shadow masks. The growing surface was studied in realtime by reflection high energy electron diffraction. The sample structure and composition were characterized ex-situ by x-ray diffraction and energy dispersive x-ray spectroscopy, while the magnetism was examined using magneto-optical Kerr effect and SQUID magnetometry. |
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T00.00192: Synchrotron Radiation Soft X-ray Spectroscopy Study of the Magnetic Anisotropy Transition in Mn3-xCoxGa Heusler Films Jeongsoo Kang, Seungho Seong, Geum Ha Lim, Woosuk Yoo, Myung-Hwa Jung, Sang Wook Han Half-metallic electronic structures predicted for some Heusler compounds [1], as well as their diverse physical properties, such as ferromagnetic, semiconducting, insulating, superconducting, and topological properties [2], have attracted much attention. When Co ions are substituted in Mn3Ga Heusler films (Mn3-xCoxGa), they are considered to be potential spintronic materials. It was found that Mn3-xCoxGa films exhibit the magnetic anisotropy transition from perpendicular magnetic anisotropy (PMA) to in-plane magnetic anisotropy (IMA) with increasing x [3,4]. But the origin of the PMA-to-IMA transition in Mn3-xCoxGa is not well understood yet.
+ kangjs@catholic.ac.kr [1] R. A. de Groot, et al., Phys. Rev. Lett. 50, 2024 (1983). [2] S. Chadov, et al., Nature Mater. 9, 541) (2010). [3] H. Kurt, et al., Phys. Rev. B 83, 020405(R) (2011). [4] Kyujoon Lee, et al., J. Alloys Compd. 858, 1582884 (2021). |
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T00.00193: Multiscale simulations toward magnetic loss and magnetic recording Hung B Tran, Yu-ichiro Matsushita Magnetic simulations for magnetic material have attracted much attention for industrial and scientific purposes by utilizing the current computational power. In this context, the multiscale simulation technique is one of the most important methods to realize the human scale (time and length) simulations while maintaining the accuracy of electronic-level calculations. We have developed a multiscale simulation platform that can tackle several important magnetic properties, such as magnetic loss and magnetic recording, with solid bridges between the methodologies [1,2]. In this study, we consider some well-known materials and compare them with experiments to demonstrate the accuracy of our methodology. Multiscale simulation is a helpful tool for searching and optimizing high-performance magnetic materials at a macro scale. |
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T00.00194: Antiferromagnetic FeTe2 Phase Formation at the Sb2Te3/Ni80Fe20 Interface Alexandria Will-Cole Topological insulators (TIs), specifically Bi1-xSbx alloys and van der Waals chalcogenides X2Q3 (X = Bi, Sb, Bi1-xSbx; Q = Se, Te) with tetradymite structure, have insulating bulk state and 2D metallic surfaces enabled by topologically protected Dirac surface states (TSS).TIs exhibit large charge-to-spin conversion efficiencies, strong spin-momentum locking, and conductive surface states making them ideal for applications in spin-orbit-torque magnetic random access memory magnetic tunnel junction devices. Bilayer TI/ferromagnet (FM) heterostructures are promising for spintronic memory applications due to their low switching energy and therefore power efficiency.Until recently, the reactivity of topological insulators with FM films was overlooked in the spin-orbit-torque literature, even though there are reports that it is energetically favorable for topological insulators to react with transition metals and form interfacial layers.The novel intrinsic topological insulator phase NiBi2Te4 was recently reported at the interface of Bi2Te3/Ni80Fe20 – thus these interfaces can host exciting new topological phases. We fabricated a bilayer TI/FM heterostructure comprised of molecular beam epitaxy grown Sb2Te3 and DC sputtered Ni80Fe20. Broadband ferromagnetic resonance revealed spin-pumping evident by significant enhancement in Gilbert damping likely a signature of the TSS or the presence of large spin-orbit-coupling in the adjacent Sb2Te3, and a reduction in the effective in-plane magnetization. With low temperature magnetometry, exchange bias is observed which is consistent with an exchange interaction between an antiferromagnet (AFM) and an adjacent FM. Upon cross-section high angle annular dark field scanning transmission electron microscopy of the interface between Sb2Te3 and Ni80Fe20 we observed a complex interface with interfacial phase formation. The predominant phase was structurally consistent with a NiTe2-type phase. Density functional theory calculations revealed that the AFM at the interface was due to the NiTe2-type structure with Fe in the Ni-site, specifically an FeTe2-1T phase. This work emphasizes the chemical complexity of TI/FM interfaces. These interfaces may host novel, metastable intrinsic magnetic topological phases and should be studied more in depth. |
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T00.00195: Structural engineering of La0.7Sr0.3MnO3 thin films - towards magnetic oxide-van der Waals heterostructures Damian Brzozowski, Yu Liu, Dennis Meier, ingrid hallsteinsen Quantum materials gain an increasing interest in the field of electronics research. One exciting opportunity is heterostructures of oxides and van der Waals materials exhibiting unique combined properties and emergent interfacial properties. Here, the first step is to ensure high-quality interfaces and the proper connectivity between inherently different crystal structures. In this work, we focus on structural engineering of ferromagnetic La0.7Sr0.3MnO3 (LSMO) as hexagonal oxide layer. Our hypothesis is that exposing hexagonal symmetry along the (111) direction promotes connectivity to the hexagonal structure of dichalcogenide. |
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T00.00196: Proximity induced ferromagnetism in spin-orbit semimetal SrIrO3 Arun Kumar Jaiswal, Dirk Fuchs, Matthieu Le Tacon, Rudolf Schneider, Di Wang, Vanessa Wollersen Magnetotransport - the change of the electric resistance with applied magnetic field - is a very powerful tool to investigate magnetism through electronic transport in ultrathin films. Magnetoresistance (MR) and the anomalous Hall resistance (AHR) in a ferromagnet directly depend on the magnetization of the ferromagnetic material as MR ≈ αH2 - βM2, and AHR ≈ γM; where α, β, γ are the proportionality constants and H, M are the external applied field and magnetization respectively. Here, we report the direct observation of strong intrinsic anomalous Hall effect with a Hall angle of ~ 0.8 % in a heterostructure consisting of SrIrO3 (SIO), a strong spin-orbit coupled semi-metal [1] and a ferromagnetic insulator LaCoO3 (LCO) [2], which limits the electronic transport exclusively to the SIO layer. Beside a hysteretic positive anomalous Hall resistance and butterfly shaped negative magnetoresistance, a four-fold magnetocrystalline anisotropy with magnetic easy axis along the [110] in-plane direction is observed below Tc ≈ 100 K [3]. The Magnetization M deduced from MR and AHR show similar field dependence and coercive field suggesting same origin of the both effects. Inserting four monolayers of insulating SrTiO3 between SIO and the LCO completely suppresses Tc, evidencing proximity induced ferromagnetism in SrIrO3. |
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T00.00197: Antiferromagnetic and relaxor-type ferroelectric behavior in iron doped GdCrO3 Jacob Pfund, Jianhang Shi, Mohindar S Seehra, Menka Jain Here we present the comparative study of the structural, magnetic and dielectric properties of 960 nm thick film and bulk pellet of single-phase polycrystalline GdFe0.5Cr0.5O3. The film was fabricated on a platinized-silicon substrate by solution deposition and spin-coating methods. The bulk pellet was synthesized by the citrate solution route. Magnetic measurements show Néel temperature~ 270 K for both the bulk and the film whereas dielectric measurements show ferroelectric to paraelectric TC ~ 525 K for bulk and 450 K for the film. The frequency dependent dielectric data of both samples is found to follow Vogel-Fulcher relation that implies relaxor-type diffusive ferroelectric behavior. Interfacial Maxwell–Wagner polarization was also observed at low frequencies. The electric polarization hysteresis loops, although leaky, are observed at room temperature revealing multiferroic nature. Details and discussion of these results will be presented. |
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T00.00198: Spin transport in Ni81Fe19/AlOx/SrTiO3 heterostructure Nozomi Soya, Takayoshi Katase, Kazuya Ando The generation and manipulation of a spin current is fundamental for the spintronics devices. The conversion phenomena between spin and charge currents in solids have been intensely investigated in a wide variety of systems. One of the promising candidates is the two-dimensional electron gas (2DEG) in SrTiO3-based structures with a strong Rashba spin-orbit coupling. In a Rashba system, an in-plane charge current generates a transverse spin density, which is known as the Edelstein effect (EE). An efficient spin-to-charge conversion through the inverse EE has been demonstrated in metal oxide/SrTiO3 heterostructures with 2DEGs at the interfaces. However, evidence for the charge-to-spin conversion, a technologically more important process, has been lacking. Furthermore, the spin transport mechanism in this system has been unclear. |
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T00.00199: Magneto-Optic Measurements of Sputtered Thin Films with Perpendicular Magnetic Anisotropy Zeynep Alptekin Layering Co and Pt is a known way to make magnetic thin films that display perpendicular magnetic anisotropy (PMA). Such films are useful in data storage and in spin-transfer torque devices. PMA is also a critical component to a proposed tunable spintronic terahertz emitting device where a layer with PMA will serve as a source of out-of-plane spin current upon ultrafast demagnetization from an intense laser pulse. As Pt is a heavy, 5d metal, it will scatter the spin current, and hence the top Pt layer must be replaced by a lighter metal, potentially resulting in an undesirable reduced PMA. We grew multi-layered samples using DC and RF sputter deposition on silicon substrates with a 1 nm Ta seed layer following parameters presented in literature [1], and achieved similar polar coercive field (Hcoer) results of about 15 mT while retaining a high degree of remanence. We examined two main variations: (1) a single Co layer: Pt2/Co1.2/Pt2 vs. Pt2/Co1.2/Cu2 vs Pt2/Co1.2/Pt2/Cu2 and (2) double Co layers: Pt2/Co1.2/Pt2/Co1.2/Cu2. The thickness per layer in nm is the number after each element. Hcoer of the (1) variation were 15.5 mT, 3.54 mT, and 11.6 mT, respectively. Hcoer of the (2) variation was 25.7 mT. Our results bode well for the path forward for the spintronic structures with strong PMA that also enable spin current transport for non-local manipulation of spin dynamics. |
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T00.00200: Reconfigurable Spin-wave Dispersion in Continuous Magnetic Layer Induced via Artificial Spin Ice Magnonic Crystal Troy Dion, Hidekazu Kureyabashi, Will R Branford, Takashi Kimura, Jack C Gartside, Daan M Arroo, Alexander L Vanstone, Kilian D Stenning Spinwaves are proposed as next generation information carriers to supersede transistor based computing technologies which are approaching fundamental physical limitations. Spinwave dispersions can be tuned by spatially modulating the properties of the materials through which they propagate, so-called magnonic crystals [1]. Flexible functionality via reconfigurability is a desirable property. Artificial spin ice (ASI) is an arrangement of magnetic nanoislands already showing promise for reservoir computing [2]. Spinwave propagation in nanostructures is inefficient due to dipole-coupling. Iacocca et al. demonstrate increased interisland coupling via a continuous magnetic underlayer [3]. Similarly, we propose ASI as a magnetization modulator of an efficient spinwave supporting media. Using different microstate and underlayer magnetisation directions we demonstrate band gaps, spin-wave non-reciprocity, important for spin-wave diode realisation, and spinwave propagation suppression. Nonreciprocity can be further enhanced by differential fabrication of nano island geometry which also allows access to all microstates with simple fields protocols. |
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T00.00201: Thin film growth of 3D antiferromagnet NdFeO3: spin hall magnetoresistance as a special probe for film-characterization Aditya A Wagh, Priyanka Garg, Suja Elizabeth, P S Anil Kumar In past few years, insulating 3D antiferromagnets (AFM) that exhibit spontaneous net magnetic moment (weak ferromagnetism due to spin-canting) are gaining attention from the spintronics community. Notably, the net moment and Neel vector, both provide handles for manipulating spin transport via external magnetic field making these materials a promising choice for exploring novel antiferromagnetic spintronics devices. Recent spin transport studies on single crystalline 3D AFMs, DyFeO3 and Ho0.5Dy0.5FeO3 have highlighted usefulness of spin Hall magnetoresistance (SMR) as a probing for the magnetic anisotropy [1, 2]. |
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T00.00202: Self Spin-Orbit Torque in Ferromagnetic Metals Ryan W Greening Understanding spin current generation in ferromagnetic heavy-metal bilayers is essential for commercialization of spin-orbit torque devices and is a subject of scientific interest. It is often assumed that in a ferromagnetic heavy metal bilayer the spin current is generated by the spin Hall effect in the heavy metal or via interface effects between the layers. The role, if any, of the ferromagnet has been neglected. Recently, it has been shown that a ferromagnetic metal may itself generate spin accumulation at the interface of a ferromagnet, resulting in a measurable anomalous spin-orbit torque [1]. In this poster, we will demonstrate an experimental mechanism for generating a net spin-orbit torque arising solely from the spin hall or interface effects in a ferromagnetic bilayer system. |
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T00.00203: Chirality-dependent second-order spin current in systems with time-reversal symmetry Ryosuke Hirakida, Masao Ogata The spin polarization phenomenon called chirality-induced spin selectivity (CISS) has recently attracted much attention. CISS was first discovered in DNA in 2011 and has been intensively studied in organic molecules. CISS in DNA has been reported to produce spin polarization rates of up to 60% and is expected to be applied to efficient spin current generation technology in the future. In 2020, it was shown that CrNb3S6, an inorganic crystal, also shows CISS. |
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T00.00204: Visualization of spin-wave propagation dynamics using laser-free GHz stroboscopic transmission electron microscopy Chuhang Liu, Spencer A Reisbick, Myung-Geun Han, Alexandre Pofelski, Chunguang Jing, Yimei Zhu Spin waves, also known as magnons, have the potential to play a vital role as information carriers in spintronics. Their lower energy damping, short wavelength and spin intrinsic nature, promise high-speed data processing in conventional and quantum information transmission. Although several experimental techniques have already been applied to study magnons, imaging spin wave dynamics with sufficient spatial resolution remains a challenge. |
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T00.00205: Magnetic phase diagram and thermodynamic study of CuB2O4 Meng-Jung Hsieh, Jiunn-Yuan Lin Numerous studies on copper metaborate (CuB2O4) in the parametric space of magnetic |
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T00.00206: Coexisting ferromagnetic component and negative magnetoresistance at low temperature in single crystals of the VdW material GaGeTe ATANU ROYCHOWDHURY We report magnetoresistance and magnetization studies of single-crystal GaGeTe, which has been proposed as a Van der Waals material. Semi-metallic character is observed in the temperature (T) variation of resistivity (ρ), following ρ(T) ∝ T2 at low temperature with a slope compatible with the usual spin-fluctuating system. Magnetoresistance (MR) at 2 K is negative and strongly dependent on the direction of the magnetic field (H) with respect to the crystallographic c-axis. MR changes sign with increasing temperature above ∼ 100 K, when H is applied along the c-axis. Hall measurements indicate the p-type conductivity with a considerable hole concentration of ∼ 8.7×1019 cm−3. Angle-resolved photoemission spectroscopy reproduces the reported results and confirms a peculiar dispersion shape of the hole-like band at the bulk high-symmetry T-point near the Fermi energy indicating band inversion. Magnetic hysteresis measurement at 2 K shows diamagnetic behaviour at high-H, whereas a ferromagnetic (FM)-like magnetic hysteresis loop is observed at low-H in between ± 4 kOe. The FM component disappears at 4 K. Signature of spin-fluctuation in ρ(T), negative MR, and low-T FM component without conventional 3d or 4f impurities in GaGeTe is attractive for the fundamental interest. |
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T00.00207: Giant spin Hall effect and spin-orbit torques from 5d transition metal - aluminum alloys for energy efficient synthetic antiferromagnetic racetrack memories Peng Wang, Stuart Parkin Synthetic antiferromagnetic thin film stacks are an essential component for racetrack memory and magnetic tunnel junction devices. The magnetic layers in these devices must display perpendicular magnetic anisotropy (PMA) that is typically derived from interfaces between [111] crystallographically textured layers of Co and Ni. Here, we show that 5d transition metal-Al alloy sputtered thin films that display an L10 structure even for room temperature deposition both show large PMA as well as giant spin Hall effects that give rise to giant spin orbit torques. Using the L10 compound RuAl as a AF spacer layer we demonstrate novel synthetic antiferromagnets with an entire L10 structure that are, moreover, crystallographically ordered along the [001] orientation and yet demonstrate high PMA. We demonstrate state-of-the-art racetrack memory devices that exhibit a several-fold increased efficiency for current induced domain wall motion as compared to prior-art materials. These structures are formed on thin IrxAl100-x underlayers with an L10 structure and are composed of ultra-thin layers of cubic Co and Ni with the L10 RuAl as the antiferromagnetic coupling spacer layer. These structures exhibit chiral Néel -type domain walls so that all the domain walls move synchronously along the racetracks at very high speeds under the influence of nano-second long current pulses. Moreover, the domain walls show very high thermal stability after repeated motion backwards and forwards along the racetracks. These novel materials based on L10 compounds provide a new route for the multifunctional use of racetrack memories that are compatible with complementary metal-oxide semiconductor technologies. |
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T00.00208: Direct relationship of chiral spin texture induced variations of system energy and magnetization switching suhyeok an, Hyeong-Joo Seo, Eunchong Baek, Ki-Seung Lee, Soobeom Lee, Chun-Yeol You Since the chirality by the inversion symmetry breaking has been observed, systems influenced by the Dzyaloshinskii-Moriya interaction (DMI) induced chirality were actively investigated. Here, diverse reports proves that the chirality affects to the dynamic and static characteristics of spin phenomena, the magnetization switching is also no exception. However, previous findings about chirality-dependent magnetization switching just confirmed its possibility phenomenologically without consideration of presence of a deeper mechanism. |
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T00.00209: Pressure effect and magnetodielectric behavior of Néel-type skyrmion VOSe2O5 Ting-Wei Kuo The external pressure effects on a polycrystalline sample of polar Néel-type skyrmion VOSe2O5 has been investigated. Using the temperature (T) and magnetic field (H)-dependent ac susceptibility measurements, the H - T magnetic phase diagram for skyrmion boundaries has been successfully established. From DC magnetization, VOSe2O5 undergoes two magnetic ordering at TN1 = 7. 45 K and TN2 = 3.3 K. Interestingly, TN1 is increased, while the TN2 is decreased with application of external pressure (P). A four-fold enhancement of the skyrmion zone in the H-T phase diagram located in 7.2 K ? T ? 7.4 K and 16.7 Oe ? H ? 46.5 Oe at ambient pressure is enhanced to 7.4 K ? T ? 8.05 K and 14.5 Oe ? H ? 61.3 Oe at 14.2 kbar. Further, T and H-dependent dielectric (e¢) data indicate e¢ anomalies at TN1 and TN2 with the magnetoelectric coupling below TN1. Density function theory along with TB2J calculations, was employed to explore the anisotropic exchange ()as well as the Dzyaloshinskii–Moriya interaction () parameters. A significant modulation of and was found and ascribed to be a possible source for enhancing the skyrmion phase under external pressure. |
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T00.00210: Thermodynamic studies of new triangular lattice Ytterbium selenites Ravi Shankar S P N, Rabindranath Bag, Sara Haravifard Magnetic materials with frustrated lattices draw significant attention in the search for unusual phenomena such as quantum spin liquid (QSL), in which the magnetic moments are strongly correlated, and yet no long-range magnetic ordering develops at very low temperatures due to geometric frustration. Triangular lattice (TL) antiferromagnetic systems are widely explored for QSL because of their simplicity of lattice arrangement. In Heisenberg two-dimensional TL systems (S = ½), the quantum fluctuations are more robust, which suppresses long-range magnetic order (LRO) even at T = 0 K limit. We synthesized and studied the thermodynamic properties of a new family of triangular lattice Ytterbium (Yb) selenites. These results demonstrate the absence of long-range ordering down lowest temperature accessible. In this talk, we are going to present our experimental results for this triangular lattice Yb selenites. |
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T00.00211: Electronic structure and magnetism in Fe3O4 and Cr3O4 Chandra M Adhikari, Rabi Khanal, Pauf Neupane, Durga Paudyal We investigate the electronic structure and magnetism of Iron (II, III) oxide (Fe3O4) called magnetite and Chromium (II, III) Oxide (Cr3O4) to explore and understand the fundamental physics behind their physical properties and their applicability to magnetism and quantum-based technologies. The Fe3O4 has Fe in both octahedral and tetrahedral sites providing two competing structures in its crystal. The same structural behavior is expected and observed in more complex Cr3O4. We explore and predict how the 3D bulk of these transition metal oxides and their single-layer 2D counterparts behave in terms of magnetic ordering and magnetic phase transition. Fe ions interacting magnetically with non-similar sites, namely the interacting octahedral/tetrahedral pairs, yield antiferromagnetic ordering, whereas the interaction of the octahedral-to-octahedral ions is ferromagnetic, resulting in the overall ferromagnetic ordering. The comparative study of Fe3O4 with Cr3O4 is primarily interesting because of the contrasting filling of 3d orbitals in respective Fe and Cr compositions. |
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T00.00212: Physical mechanism for thermal activation of electron spin filtering and spin generation in InAs/GaAs nanostructures Y Huang, P Hojer, V Polojarvi, S Hiura, A Aho, R Isoaho, T Hakkarainen, M Guina, S Sato, J Takayama, A Murayama, Irina A Buyanova, Weimin M Chen Recently we succeeded in generating record-high conduction electron spin polarization (exceeding 90%) at room temperature (RT) in InAs/GaAs quantum dots (QDs) [1]. This was accomplished by defect-engineered remote spin filtering via an adjacent tunneling-coupled GaNAs spin filter. Opposite to the general trend seen in other approaches, the spin polarization generated by our approach is found to increase with increasing temperature up to RT, desirable for practical device applications in spintronics. In this work we show that this increase originates from a thermally accelerated remote spin-filtering effect as a result of thermally activated spin-dependent recombination via the spin-polarized spin-filtering defects, i.e., grown-in Ga self-interstitials, which selectively deplete conduction electrons with an opposite spin orientation to that of the defect electron. This conclusion is based on our experimental evidence for a direct correlation between the measured spin polarization degree and the defect-mediated non-radiative recombination efficiency over a wide temperature range, which is further supported by a detailed rate equation analysis of the spin and recombination dynamics. |
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T00.00213: Emergence of Rashba splitting and spin-valley properties in Janus MoGeSiP2As2 and WGeSiP2As2 monolayers Ghulam Hussain, Abdus Samad, Majeed Rehman, Giuseppe Cuono, Carmine Autieri First-principles calculations are performed to study the structural stability and spintronics properties of Janus MoGeSiP2As2 and WGeSiP2As2 monolayers. The high cohesive energies and the stable phonon modes confirm that both these structures are experimentally accessible. In contrast to pristine MoSi2P4, the Janus monolayers demonstrate reduced direct bandgaps and large spin-split states at K/K’. For the monolayered Janus structure, the broken mirror symmetry with respect to the Mo/W-plane gives rise to a potential gradient normal to the basal plane, which causes difference in the work function for the two surfaces. In addition, the spin textures exposed that breaking the mirror symmetry brings Rashba-type spin splitting in the systems which can be increased by using higher atomic spin-orbit coupling. The large valley spin splitting together with the Rashba splitting in these Janus monolayer structures can make a remarkable contribution to semiconductor valleytronics and spintronics. |
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T00.00214: Dynamics of Magnetic Order in Monolayer Semiconductors Andrew H Kindseth, Kai Hao, Robert T Shreiner, Alexander A High It has recently been shown that in slightly electron doped WSe2, there are spin correlations which can be stabilized by a circularly polarized optical pump, and measured using a circular dichroism measurement. In this low-doped regime, the electron-electron interactions mediate the formation of correlated phases. Using the circular dichroism, spin-correlations and their dynamics can be measured in optical pump-probe measurements. We study the spatio-temporal variation of these spin-correlations at displacements of several micrometers, demonstrating an amplification of the initial pump-induced spin-polarization by more than an order of magnitude due to magnetic interactions. Understanding of the behavior of spin-correlations in WSe2, and manipulation of spin-amplifcation, forwards efforts in the study of correlated phases in two-dimensional materials and applications in nanophotonics and spintronics. |
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T00.00215: Direct exchange-interactions boost magnetic frustration and a large zero-point entropy in magnetic diamond-lattice spinels Josep Fontcuberta, R. Trócoli, Carles Frontera, Judith Judith Oró-Solé, Clemens Ritter, Pere Alemany, Enric Canadell, M. Rosa Palacín, Amparo Fuertes Magnetic frustration is instrumental in the suppression of long range magnetic order. Spinels AB2X4, where magnetic ions exclusively occupy the tetrahedral A-sites, are examples of frustrated magnetic systems, some displaying exotic phenomena such as order-by-disorder and spiral spin-liquids, due to the presence of competing interactions among nearest-neighbors (Jnn) and next-nearest-neighbors (Jnnn) magnetic ions. E. Current understanding is based on the competing concurrence of Jinnn and Jinnnn indirect (super) exchange interactions. Here, we report structural, magnetic and calorimetric data indicating that in the new spinel nitride: MnTa2N4, N-Ta and N-Mn hybridization modulates the Jinnn and Jinnnn interactions but more importantly the direct Mn-Mn magnetic interactions are found to overrule the superexchange interactions and dramatically reinforce frustration. As a result, magnetic order only emerges at lower temperature, where only a fraction of Mn2+ spins order in a short-range degenerated spiral state. Calorimetric data reveals the presence of a large (30%) zero-point magnetic entropy. These observations, indicate an unexpected central role of direct magnetic interactions on frustration and suggest that spinel nitrides offer a new route for the research of quantum materials. |
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T00.00216: On the Magnetic Properties of Rare Earth-Based Tsai Approximants Daniel L Qvarngård In the hopes of understanding the magnetic properties of rare earth quasicrystals, extensive studies have been performed on the properties of their approximants: periodic structures which locally look like their aperiodic counterparts. Experimentally, the high temperature behavior of the susceptibility correlates with the conduction electron density, suggesting that the RKKY interaction is important. This poster presents our investigations into the magnetic properties of classical Ising and Heisenberg model hamiltonians on the approximant lattice, and discusses the possibility for extending the results to the quasicrystalline case. |
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T00.00217: Spin-induced strongly correlated magnetodielectricity, magnetostriction effect and spin-phonon coupling in helical magnet Fe3(PO4)O3 Hung-Duen Yang Helical magnets are extremely promising as they have fascinating magnetic, electric, and phononic properties. Here, we report a spectrum of simultaneously occurring and highly-entangled intriguing phenomena induced by helical spin ordering in a noncentrosymmetric and spin-frustrated system Fe3(PO4)O3. Such phenomena include magnetodielectric effect in the form of a frequency-independent pronounced dielectric peak, clear magnetostriction effect manifested as a dramatic down-turn in the thermal variation of lattice parameters, and strong spin-phonon coupling (which displays a unique anomalous hardening and softening of various phonon modes) at temperatures as high as TN=163 K. The observed dielectric peak is seemingly associated to a structural distortion via the strong magnetostriction effect. |
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T00.00218: Room Temperature Superparamagnetic Order with Colossal Magnetocrystalline Anisotropy in Aminoferrocene-based Graphene Molecular Magnets Yohannes W Getahun, Felicia S Manciu, Mark R Pederson, Ahmed A El Gendy Intensive studies are available on graphene-based molecular magnets due to their remarkable electric, thermal and mechanical properties. However, to date, most of all produced molecular magnets are ligand based and subjected to challenges regarding the stability of the ligand(s). The lack of long-range coupling limits high operating temperature and leads to short-range magnetic order. Herein, we introduce aminoferrocene-based graphene system with room temperature superparamagnetic behavior with long-range magnetic order that exhibits colossal magnetocrystalline anisotropy of 8 x105 and 3x 107 J/m3 in aminoferrocene and graphene-based aminoferrocene respectively. These values are comparable and even two orders of magnitude larger than the pure iron metal. Synthesized aminoferrocene [C10H9FeN]+ was reacted with graphene oxide prepared by the modified Hammers method and the chemical structure was characterized and confirmed by XRD, FT-IR, and Raman spectroscopy. To model the behavior of the aminoferrocene, we used density functional theory by placing the aminoferrocene molecule between two highly ordered hydroxylated sheets and allowing the structure to relax. The strong bowing of the isolated graphene sheets suggests that the charge transfer and resulting magnetization could be strongly influenced by pressure effects. In contrast to strategies based on ligands surface attachment, our present work opens new routes for future molecular magnets as well as the design of qubit arrays and quantum systems. |
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T00.00219: Spin-vibrational resonances and coupling in Ln-based single-molecule magnets in different environmentsDaria D. Nakritskaia, Sergey A. Varganov*Department of Chemistry, University of Nevada, Reno, 1664 N. Virginia Street, Reno, NV 89557-0216, United States.svarganov@unr.edu Daria Nakritskaia, Sergey A Varganov Lanthanide-based single-molecule magnets (Ln-based SMMs) are of high interest because of their potential applications as qubits and building blocks for high-density memory materials. One of the main challenges is increasing the spin relaxation and decoherence times, which requires detailed understanding of the electronic structure and spin dynamics in Ln-based SMMs. Most electronic structure calculations are done on isolated SMMs assuming ideal gas conditions whereas the experiments are performed in the condensed phase environments. Interaction between electron spin and molecular vibrations is one of the important mechanisms responsible for spin relaxation and decoherence. The rate of spin relaxation depends on the presence of spin-vibrational resonances and on the magnitude of spin-vibrational couplings which are affected by their environments. We investigate these effects in Ln-terpyridine complexes using ab initio multireference electronic structure methods. The calculations are performed on the molecular structures sampled from the molecular dynamics simulations in the gas, solution, and crystal phases. While in many cases energies of the spin and vibrational transitions are not significantly affected by the SMMs environment, coordination of the solvent molecules to Ln can lead to a large increase of magnetic anisotropy barrier. This effect can improve the magnetic properties of Ln-based SMMs in solutions and open new direction in designing high-temperature SMMs. |
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T00.00220: Magnon interactions in anisotropic Ising chains. Cesar A Gallegos, Alexander L Chernyshev Experiments and simulations of the quasi-1D Ising-chain ferromagnet CoNb2O6 in a polarized transverse field have shown evidence of a quasiparticle breakdown. We use spin-wave theory beyond the linear treatment to capture magnon interactions in the paramagnetic phase. We investigate decay processes and unphysical divergences in the spin-flip spectrum produced by Van Hove singularities in the 2-magnon density of states, which are regularized via a self-consistent treatment. We further explore various symmetry-allowed exchange terms in the spin Hamiltonian that can be relevant to different Ising-like chains such as BaCo2V2O8 and SrCo2V2O8. |
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T00.00221: Effects of temperature cycling on domain wall pinning in Py/Gd ferrimagnetic multilayers Liyan Jacob, Shawn Pollard Due to their potential applications in high speed, low power spintronic devices, ferrimagnetic domains and domain structures have garnered intense interest in recent years. Of particular interest is the tunable environment of ferrimagnets combined with the interactions between magnetic quasiparticles, such as vortices, and external fields or currents. In our work, we explore the response of microstructured Permalloy (Py)/Gadolinium(Gd) ferrimagnetic multilayers utilizing Kerr microscopy as a function of composition and temperature. As expected, for increasing Gd layer thicknesses beyond the compensation point, the coercivity decreases. Similarly, for Gd-doped films, we observe decreasing coercivity at higher temperatures. Through direct imaging of the magnetic domain structure as a response to the external field, we see that this decrease with temperature results in significantly weaker pinning effects, suggesting a strong influence of the Gd sublattice on pinning in artificial ferrimagnetic multilayers. Through small temperature variations, depinning can be induced without changes to the external magnetic field. |
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T00.00222: Enhanced domain wall motion by surface acoustic waves Jintao Shuai, Luis Lopez-Diaz, John E Cunningham, Thomas A Moore Domain walls (DWs) in thin films with perpendicular magnetic anisotropy (PMA) are promising information carriers for the next generation of data storage and logic operation devices.[1, 2] However, controlling DW motion efficiently remains unsolved. Here, we performed micromagnetic simulations (Mumax3) demonstrating an enhanced DW velocity in a PMA film using dynamic strain introduced by travelling surface acoustic waves (SAWs) within the creep regime. Pinning sites were created by introducing anisotropy disorder (1% and 3%). The results show that the DW velocity decreases as the SAW frequency increases from 50 to 200 MHz in the thin film with lower anisotropy disorder (1%). On the contrary, DW velocity increases with the increasing SAW frequency for the thin film with a higher anisotropy disorder of 3%. The dynamic strain waves create a dynamic energy landscape and introduce spin rotation. The period of the SAW-induced spin rotation depends on the SAW frequency. The spin rotation, on the one hand, enhances the possibility of the domain depinning from the pinning sites (for higher anisotropy disorder); on the other hand, also causes energy wastage (for lower anisotropy disorder). |
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T00.00223: Current-induced domain wall motion in the van der Waals ferromagnet Fe3GeTe2 Wenjie Zhang, Tianping Ma, Binoy Krishna K Hazra, Abhay Kant Srivastava, Stuart Parkin Magnetism in two-dimensional (2D) materials has attracted much attention, especially the recently observed stabilization of magnetic chiral nanostructures (Adv. Mat. 34.11 (2022): 2108637) in the high Curie temperature ferromagnet Fe3GeTe2. These magnetic nanostructures are promising as potential memory bits for next-generation spintronic devices, such as racetrack memory. Here, the current-induced magnetic domain wall in exfoliated few-layer thick Fe3GeTe2 flakes is investigated using variable temperature Kerr microscopy. Triggered by nanosecond current pulses, spin-transfer- and spin-orbit- torques are found to induce reliable and efficient domain wall motion. Going beyond conventional ferromagnetic metals, the clear observation of current induced domain wall motion demonstrates the potential of 2D magnetic materials for spintronics applications. |
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T00.00224: Simulation of Transport through Graphene Quantum Dots Coated with Single-Molecule Magnets Samuel I Felsenfeld, DaVonne Henry, Amjad Alqahtani, Paola Barbara, Amy Y Liu Single molecule magnets have promising potential applications as a form of new high density magnetic memory due to their small size. Here we aim to show that the spin-valve effect can be used to read the magnetization of single molecule magnets deposited on top of a graphene quantum dot. By simulating such a system with a tight binding model using the Kwant quantum transport package [1], we show that distinct current levels are visible depending on the orientation of the magnetization of the molecules. While the relationship between these current levels and the bias voltage across the dot is complicated, it could provide a way to observe the magnetic state of the molecules via transport measurements. |
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T00.00225: Electronic and magnetic properties of building blocks of Mn and Fe atomic chains on Nb(110) Krisztian Palotas, Andras Laszloffy, Levente Rózsa, Laszlo Szunyogh Magnetic impurities on a superconducting surface create so-called Yu-Shiba-Rusinov (YSR) states. In magnetic atomic chains, hybridized YSR states develop into bands that can give rise to topological superconductivity and Majorana bound states [1]. Beck et al. recently demonstrated that the YSR states hybridize not only for ferromagnetic but also for antiferromagnetic Mn atomic dimers on a Nb(110) surface due to the presence of spin-orbit coupling [2]. Motivated by this, in the present work the electronic and magnetic structures of Mn and Fe building blocks of atomic chains on a Nb(110) surface are analyzed based on theoretical calculations [3]. Most notably, a spin-spiral ground state is obtained for Fe chains along the Nb[1-10] direction due to the frustration of the isotropic exchange interactions. Here, a flat spin-spiral dispersion relation is identified, which can stabilize spin spirals with various wave vectors together with the magnetic anisotropy. |
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T00.00226: Magnetic property and controlled growth of C-Plane oriented antiferromagnetic Mn3Sn thin film Ahamed Raihan, Jyotsna Das, Ravinder Kumar, Dereje Seifu Gian anomalous Hall effect has been recently reported in antiferromagnets with almost zero net magnetization. This work presents the structural and magnetic properties of noncollinear hexagonal antiferromagnetic Mn3Sn thin films heteroepitaxial grown on MgO (111) substrates with a Ta capping layer. Co-sputtering techniques are used to prepare these samples. High-temperature annealing was done to get the crystallinity. The crystallographic orientations of Mn3Sn were considerately affected by substrate and post-annealing temperature. XRD, XPS, and Raman measurements were conclusive for the prepared thin film. The Mn3Sn films were crystallized with the c-axis preferred (0001) crystal orientation in the hexagonal D019 structure. The films were homogeneous chemically and continuously. To perform the magneto-transport measurements millimeter size Hall bar device is fabricated using a mask, not by using lithography and resist. The transport measurements have been done at different temperatures from T = 4 - 300K. The film showed weak ferromagnetism in-plane. Additionally, the exchange bias effect was studied in Mn3Sn/Py bilayers. Exchange bias fields up to 10 mT can be achieved at 4 K. In antiferromagnetic spintronics applications, Mn3Sn films are an appealing material. |
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T00.00227: Molecular Nano Magnets induced current suppression in a Ta/NiFe/AlOx/NiFe/Ta Magnetic Tunnel Junction Molecular Spintronic Device (MTJMSD) Marzieh Savadkoohi, Andoniaina M Randriambololona, Eva Mutunga, Pawan Tyagi Molecular magnetic materials can make a fundamental link between spintronic and molecular electronics. Using molecular components, electronics can reach its ultimate scale limit with properties of bulk magnetic materials while exploiting quantum effects. Single Molecule Magnets (SMM) can manipulate spins and charges and enhance memory devices and information processing. This Research investigates a magnetic tunnel junction-based molecular spintronic device (MTJMSD) in which single Molecule Magnets are attached to the exposed edges of ferromagnetic electrodes (FMEs) and act as conducting bridges. The fabricated MTJMSD is made of Ta(5nm)/NiFe(10nm)/AlOx(2nm)/NiFe(5nm)/Ta(5nm). Magnetic molecules can be coupled to the ferromagnetic electrodes weakly or strongly based on the energy difference at the barrier between molecules and contacts. Our experimental transport studies show current suppression to |
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T00.00228: Interplay between magnetic coupling and spin–orbit torque in current induced exchange bias manipulation in Pt/Co/IrMn heterostructure Eunchong Baek, suhyeok an, Soobeom Lee, Dongryul Kim, Jun-Su Kim, Ki-Seung Lee, Chun-Yeol You In recent years, several experimental results consistently show switching of perpendicular exchange bias by spin–orbit torque (SOT), which is induced by electric current via spin–orbit coupling, in heavy metal (HM)–ferromagnet (FM)–antiferromagnet (AFM) heterostructure. However, no consensus has been reached on the detailed mechanism behind the SOT induced uniaxial exchange bias switching owing to the complex interplay between SOT, exchange coupling of FM-AFM, and thermal fluctuation. |
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T00.00229: Micromagnetic simulations of spin wave interactions in comb-shaped structures Adair A Brown, Jason Liu The field of magnonics consist of investigating the use of spin waves for magnetic devices. Spin waves are the propagating disturbances of magnetic moments in magnetic materials and can be used to transfer information without the Joule heating associated with conventional current. Understanding how spin waves interact in various geometric configurations can allow for the modulation or excitation of spin waves with specific frequencies or wavelengths. In the work presented here, we have investigated spin waves in rectangular (25 μm x 100 μm) comb-shaped Permalloy microstructures with micromagnetic simulations. The structures consist of two, three, four, and five teeth with different aspect ratios (teeth width/teeth separation) that converge into a large continuous region. Spin waves were excited in the teeth by reproducing the Oersted field generated by a microstrip antenna and observed in the surface wave and forward volume wave geometry. The spin waves that propagated into the continuous region show radial emission from the teeth, analogous to the diffraction of light in a multi-slit optical experiment. We will also discuss ongoing microwave and optical experimental work with similar structures that were fabricated with laser lithography. |
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T00.00230: Probing Ultrafast Spin Dynamics in Heusler Thin Films with Extreme Ultraviolet Light Anya Grafov Extreme ultraviolet (EUV) light produced through high harmonic generation enables time- and element-resolved spectroscopy on femtosecond timescales. We utilize a tabletop EUV beamline for spectroscopic measurements of spin dynamics in magnetic materials. In particular, we investigate the behavior of Heusler alloy thin films in response to laser excitation. Such materials can have a wide variety of tunable magnetic and electronic properties as a result of their complex band structures. We can simultaneously probe these dynamics across multiple elements within a material, allowing us to uncover new coupled spin-charge-phonon-photon behaviors. Furthermore, we implement a noise-cancelling scheme to achieve precise measurements approaching the shot noise limit. |
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T00.00231: Ultrafast angular momentum relaxation dynamics studied with transient gratings Nupur N Khatu, Filippo Bencivenga, Laura Foglia, Bjorn Wehinger, Riccardo Cucini, Pietro Carrara, Stefano Bonetti The most debated question in the field of ultrafast magnetism in metallic ferromagnets, still not fully answered after almost 30 years of research is: how is angular momentum dissipated after ultrafast demagnetization? Several explanations have been put forward, and it is believed that a full picture requires multiple considerations which include the electronic, lattice and spin degrees of freedom in the materials. However, in many cases, the explanation is rather qualitative. In order to answer this question, we use a novel technique, the transient grating (TG) technique, which has been proven to be a sensible tool for studying ultrafast magnetization dynamics [1,2]. The time-dependent response induced by nanoscale extreme ultraviolet gratings in CoGd shows clearly different relaxation dynamics depending on the beam polarization and the detection geometry, suggesting a yet undisclosed intermediate relaxation mechanism for the angular momentum. Our all-optical TG experiments showed similar results in both cases, but at a longer timescale due to the micrometer level gratings. We will investigate this further by performing TG experiments at resonance and at off-resonance on different samples. We can only speculate at the moment, but new measurements comparing transient polarization and intensity grating may offer us a completely novel view of the physics at play, helping us uncover, quantitatively, the role of the two most prominent scattering channels, i.e. the phonon and magnon systems. |
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T00.00232: Enhancement of Dzyaloshinskii-Moriya interaction in Pt/CoFe(B)/MgO structure by suppression of FePt phase according to boron addition Jun-Su Kim, Gukcheon Kim, Jinwon Jung, Kuyoul Jung, Junghyeok Kwak, Jaehun Cho, Eunji Lim, Woo-Yeong Kim, June-Seo Kim, Jinyong Jung, Soobeom Lee, suhyeok an, Eungchong Baek, Dongryul Kim, Sanghoon Kim, Chun-Yeol You Here, we present the trend of the surface DMI (DS = D tCoFe(B)) according to the boron concentration in Pt/CoFe(B)/MgO structure, showing sharp increase (0.6 to 1.7 pJ/m) at 0~ 4 %. Such unexpected increase is interpreted with the FePt phase between Pt and CoFe(B) layer. Through the x-ray diffraction (XRD) analysis, we confirmed that the disordered fcc FePt phase exists in the CoFe (boron 0%) sample. It was also confirmed that the phase is remarkably decreased by small addition of boron (4 %) into the CoFeB layer. The correaltion between the fraction of FePt and DS of the system could be interpreted based on the lower work function difference between nonmagnetic and ferromagnetic metals. Comparison of DS according to the presence or absence of FePt spacer was carried out in the Pt/(FePt)/Fe/MgO structure, and a trend similar to that of the above experiment was confirmed. |
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T00.00233: Ultralong 100 ns Spin Relaxation Time in Graphite at Room Temperature Bence G Markus, Martin Gmitra, Balázs Dóra, Gábor Csosz, Titusz Fehér, Péter Szirmai, Bálint Náfrádi, Viktor Zólyomi, László Forró, Jaroslav Fabian, Simon Ferenc The emergence of spintronics technology is the driving motivation for understanding spin dynamics in 2D materials. Graphite, which has recently relaunched the interest for 2D materials, has been intensively studied, yet the electron spins dynamics remains an unresolved problem even 70 years after the first experiments. The central quantities, the longitudinal T1 and transverse T2 relaxation times were postulated as equals, which is the case for standard metals, but T1 has never been measured for graphite. Here, based on a detailed band structure calculation included spin-orbit coupling (SOC), we give a full description of the relaxation times. We have measured the T1 in graphite by saturation ESR measurements and find it markedly different from T2. We observe that spins injected with perpendicular polarization with respect to the graphene plane have an extraordinarily long lifetime of 100 ns at room temperature. The spin diffusion length across graphite planes is thus expected to be ultralong, on the scale of 70 um, suggesting that thin films of graphite --- or multilayer AB graphene stacks --- can be excellent platforms for spintronics applications compatible with 2D van der Waals technologies. Finally, we provide a qualitative account of the observed spin relaxation based on the anisotropic spin admixture of the Bloch states in graphite obtained from DFT calculations. |
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T00.00234: Magnetism and electronic band properties of NiFeMnAl Heusler alloy Jax G Wysong, Gavin M Baker, Paul M Shand, Pavel Lukashev, Parashu R Kharel Heusler alloys exhibiting half-metallic or spin gapless semiconducting (SGS) properties have become attractive materials for spin-transport-based devices. This is due to their ability to have tunable magnetic properties and high Curie temperatures well above room temperature. We have investigated one such material, NiFeMnAl, which is predicted to show SGS properties. We have synthesized NiFeMnAl alloy using arc-melting in an argon environment. X-ray diffraction patterns indicate that the as-prepared sample has a single-phase cubic crystal structure with disorder. The isothermal magnetization measurement M(H) carried out at 100 K shows a saturation magnetization of about 54 emu/g. The thermomagnetic M(T) measurement shows that there is a single magnetic transition at its Curie temperature of about 460 K. We will also discuss the effect of heat treatment and the results of first principles calculations. |
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T00.00235: Control of Interfaces in Magnetic Tunnel Junctions Daniel Bernstein, Ilyas Farhat, Christopher Alpha, Ella Gale, Abdel F. Isakovic Magnetic tunnel junctions, or MTJs, have been an important nanodevice in spintronics and applications. A number of MTJ parameters have been studied and explored in detail in an attempt to fully understand and better control these devices. With this, MTJs have been made increasingly complex over the years, with an increasing number of layers, and layers with various chemical properties. Here, the focus with MTJs, is analyzing and minimizing the energy of operation and switching, so the complex junctions were foregone in favor of the traditional trilayer designs. One key step in controlling the energy needed to operate these junctions is exploring changes in the surface geometries of these layers. Breaking symmetry at the surface of the crystal structures in ferromagnetic layers contributes to changes in the magnetic anisotropy of the layers. Because of this, the change in anisotropy leads to a change in the required switching energy for the junction, which we demonstrate in this work. While many materials can be used for the layers in the MTJs, the samples explored were FeCo, MgO and Fe layers. As a result of this these trilayer junctions have a magnetoresistance from 60% to 200%. |
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T00.00236: Helimagnet-based Non-volatile Multi-bit Memory RABIUL ISLAM, Guoxing Miao, Peng Li, Marijan Beg Existing semiconductor-based memory devices suffer from high power, low density, and lack of multi-bit capability. To overcome these limitations, emerging memory technologies based on spatially varying spin textures, such as helimagnets and skyrmions, are promising. In this work, we propose a helimagnet-based memory that can store multi-bits of information. The memory device consists of a helimagnet layer sandwiched between two ferromagnetic layers that are used to lock the spin configurations. The bottom pinned layer consists of large anisotropy energy that can fix the bottom layer spin configuration to a set axis, and the top free layer can rotate under applied in-plane fields. We first find the relaxed spin structure, resulting from competition between DMI and exchange energy, and it is defined as an equilibrium state (“0”). The writing of a memory state is simulated by using an in-plane field that will rotate and transform the spin configurations of the memory device. Our results show that stable configurations can be at rotations of an integer multiple of 180 degrees (corresponding to states “-2”, “-1”, “1”, “2”, etc.), where anisotropy stabilizes the free layer. An intermediate unstable spin configuration tends to revert to its adjacent state. Simply by changing the field in a different direction, i.e., toggle switching, we could achieve multi-bit data storage per unit memory cell. |
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T00.00237: Magnetic Field Sensor Based on a Spin-Wave Interferometer with a Positive Feedback Alexander Khitun We demonstrate experimentally the operation of a spin-wave magnetometer integrated into a circuit with a positive feedback. The circuit consists of passive magnetic and active electric parts. The magnetic part include a sensing element, which is a magnetic cross junction made of Y3Fe2(FeO4)3. The electric part includes a non-linear amplifier and a phase shifter. The electric and magnetic parts are connected via micrometer size antennae. Spin waves are excited by two of these antennae while the output inductive voltage produced by the interfering spin waves is detected by the third antenna. Spin waves propagating in the orthogonal arms of the cross may accumulate significantly different phase shifts, depending on the direction and the strength of the external magnetic field. The output inductive voltage reaches its maximum in the case of constructive spin wave interference. The positive feedback provides further signal amplification. It appears possible to enhance the response function, compared to the passive circuits without a feedback, by a factor of ×100 without an increase in the noise level. The experimental data show a prominent response to the external magnetic field variation, exceeding 5×103 V/T . At the same time, the intrinsic noise spectral density of the device can be as low as 10-16 V2/Hz. The estimated sensitivity of the presented prototype is 2×10-12 T/√Hz. at room temperature. We argue that spin-wave magnetometers can potentially be as sensitive as SQUIDs while operating at room temperature. |
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T00.00238: Origin of spin reorientation in Nd2Fe14B permanent magnet Yu-ichiro Matsushita, Hung B Tran The spin reorientation in Nd2Fe14B, which is the host crystal of the well-known neodymium permanent magnet, is thought to originate from the crystal field effect and is usually studied by an empirical model with parameters extracted from magnetization data of the experiments. However, in this study, we found, for the first time, that the spin reorientation in Nd2Fe14B is caused by Dzyaloshinskii–Moriya interactions. Our simulations successfully reproduce the peak-like of magnetic anisotropy energy in the experiment without any empirical parameter. Furthermore, we found that the spin reorientation in Nd2Fe14B results in the rotating magnetocaloric effect, which might be used for practical applications. We also found that the Dzyaloshinskii–Moriya interactions non-negligibly contribute toward the physical properties of magnetic materials. |
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T00.00239: Investigation of the non-linear magnetoelectric responses of hexagonal ferrite Zn2Y Yuzan Xiong, Hongwei Qu, Rao Bidthanapally, Gopalan Srinivasan In this study, nonlinear magnetoelectric (NLME) responses of Y-type hexagonal ferrite Zn2Y to both magnetic and electrical fields were investigated. The observation and measurements of the strong magnetic response was conducted on a well-designed waveguide fabricated with help of photolithography. The hexagonal ferrite was placed at an optimized location for desired response. With an external in-plane magnetic field excitation ranging from 200 Oe to 2800 Oe, a total frequency shift of ~ 10 GHz was observed in the transmission coefficients. By applying an in-plane DC current of 9 mA to the ferrite through metalized pads along the signal direction in the Zn2Y sample, at the center frequency of 9.8 GHz, a 1.2 GHz shift was measured. The results in this study demonstrate the dual tunability of the magnetic response of Zn2Y, suggesting its potential applications in frequency control in X band and beyond. |
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T00.00240: Voltage-Controlled Translational Motion of a Magnetic Skyrmion: a Magnetic Skyrmion Transistor Seungmo Yang, Chanyong Hwang, Jong Wan Son, Tae-Seong Ju, Duc Minh Tran, Hee-Sung Han, Sungkyun Park, Bae Ho Park, Kyoung-Woong Moon Since its experimental demonstration at room temperature, magnetic skyrmions have been intensively studied as one of novel information carriers because of their unique topological characteristics. Although many skyrmion devices—including a skyrmion racetrack memory, a skyrmion synapse device, and a skyrmion reshuffler—have been reported, voltage-controlled skyrmion devices have rarely been reported. Here, we demonstrate the spatial uniformity of voltage-controlled magnetic anisotropy. Using this technique, we prove that the shape and topology of a skyrmion are well-maintained when passing through two different anisotropy areas. Finally, a proof-of-concept experiment of a skyrmion transistor is presented, which has never been demonstrated experimentally. Our findings will open a new route toward the design and realization of skyrmion-based devices in the near future. |
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T00.00241: Study of Magnetostructural Phase transitions and Magnetocaloric Effects in Mn65-xGa17C18+x (x = 0, 1, 3, 4) Abhiyan Oli A variety of magnetic materials show several properties, such as magnetic shape memory, large magnetoresistance, Hall Effect and magneto caloric effects. Several of these materials, also shows potential application in magnetic refrigeration technology. For example, the ternary alloy system Mn-Al-C (Al=Zn=Sn=In) exhibits face centered cubic ternary phase and has spontaneous magnetization. Recently it has been found that a similar magnetic ternary phase also occurs in the Mn-Ga-C system. Here we will present our results on structural, magnetic and magnetocaloric properties of Mn65-xGa17C18+x (x =0,1,3,4) compounds. Detailed X-ray diffraction (XRD), and magnetization measurements will be shown. The occurrences of the structural transition, magnetic entropy change, magnetoresistance will be presented and discussed. |
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T00.00242: Self-Assembly as a Tool to Study Microscale Curvature and Strain-Dependent Magnetic Properties Balram Singh Geometrical transformations, such as rolling a 2D ferromagnetic film into a 3D cylinder provide means to tune its magnetic properties generating different magnetic ground states. Rolled-up magnetic membranes with azimuthal magnetic anisotropy are very attractive due to expected much higher domain wall velocity (compare to their planar counterparts) and for applications as impedance based field sensors. However, a clear recipe for acquiring highly mobile azimuthal domains in a soft ferromagnetic tubular geometry is unclear. State of the art studies report the rolling of an extended ferromagnetic film (of hundreds of micro-meters), which after rolling converts into tubular geometry with 2-3 windings. Changes in the magnetic domain configuration in such tubular geometries may arise from modifications of the shape anisotropy in addition to stress-induced anisotropy due to rolling. In our work,[ref.] we report on rolling-induced azimuthal anisotropy in Ni78Fe22 stripes purely due to strain, considering that curvature induced changes in shape anisotropy can be neglected due to reduced dimensions of our magnetic stripe in the azimuthal direction. For that, we employed a self-assembly rolling technology based on a polymeric platform, which allows choosing the shape and size of the magnetic structure willingly. Magnetic structures patterned on the polymeric platform can be bent controllably and hence the sign and magnitude of strain on the magnetic structure can be adjusted. We quantify the induced azimuthal magnetic anisotropy by electrical measurements capable of providing magnetic properties of magnetic structures hidden under the 3D polymer architecture. |
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T00.00243: SEMICONDUCTORS, INSULATORS, AND DIELECTRICS Alexandria Cannon
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T00.00244: Light Scattering on Gold Nanosphere Irina V Bariakhtar The systems of nanoparticles absorbed on the substrate are of the practical interest now due to the multiple applications of these systems in nanosensors, waveguides, electronic devices and lately in PV elements for improving of their efficiency [1]. Such quasi-two-dimensional systems show novel properties and behavior that is different from the bulk material properties and are of a particular interest of the nowadays experimental tasks. |
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T00.00245: Giant enhancement of photoluminescence emission in band-engineered type I TMDC/PbI2 heterostructure by nonradiative energy transfer PRAHALAD K BARMAN, Saroj Poudyal, Bubunu Biswal, renu yadav, Abhishek Misra Monolayer transition metal dichalcogenides (TMDCs) display the robust nature of excitonic or trionic photoluminescence (PL) emission due to direct bandgap nature, which can be enhanced by changes in the environment and the chemical potential of the material. However, a drastic PL quenching has been observed when TMDCs are stacked in van der Waals heterostructures and forming type II band alignment, which favors the nonradiative recombination of photocarriers. Herein, we have achieved an enhancement of the photoluminescence of monolayer MoS2 (and MoSe2) on top of a few layers PbI2 (forming van der Waals heterostructures) at resonance conditions in a room temperature regime. TMDC/PbI2 forms type I band alignment, which preserves light emission of MoS2 against nonradiative interlayer recombination processes. TMD monolayer can be enhanced by a factor of ~ 30 depending on the excitation wavelength. We have observed the enhancement of trion ~ 20 times compared to the monolayer TMDCs. Charge transfer and energy transfer both play crucial roles in the enhancement process. Furthermore, interlayer dipole coupling induced nonradiative Fo¨rster resonance energy transfer (FRET) process could be the possible reason of having such high enhancement of emission from TMDCs. Therefore, the present results of type I van der Waals heterostructures are highly promising materials for ultralight and ultrathin optoelectronics applications. |
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T00.00246: Drift and funnel effects of trions in suspended MoSe2 monolayer Woo Hun Choi, Seong Won Lee, Su Hyun Gong Exciton transport in transition metal dichalcogenides (TMDCs) has been studied for the realization of TMD-based optoelectronic devices. However, because of their charge-neutral nature, electric control of the exciton's motion is expected to be not viable. Also, the quick recombination process of electrons and holes further hinders the transport property. In the case of charged excitons (trions), the direct control of their transport using electric-fields can be employed, analogous to conventional electronic devices. In this work, we demonstrate the drift and funnel effects of free trions in a suspended MoSe2 monolayer by exerting a static electric field. To do so, we fabricated a simple electromechanical device to control the electric fields, which increases the trion density by electrical doping and pulls down the monolayer simultaneously. We confirm that under the influence of electric force, locally excited trions were dragged and consequently funneled toward the center of the strained layer. Our research provides a direct way of controlling free trion motion and opens up the possibility for the application of trion-based optoelectronic devices. |
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T00.00247: Exciton-polariton properties in hBN-encapsulated transition metal dichalcogenides Ho Seung Lee, Junghyun Sung, Su Hyun Gong Two-dimensional (2D) transition metal dichalcogenides (TMDCs) have been remarked for their outstanding potential in photonics and optoelectronic devices. 2D TMDCs shows strong light-matter interactions due to increased excitonic effect in 2D limits and valley degrees of freedom as a result of broken inversion symmetry. These unique properties of TMDCs have led to studies of exciton-polaritons (EPs) demonstrated by cavity engineering. Further studies have shown that the formation of EPs is possible even in a bare structure of TMDCs due to their strong exciton-photon coupling. Hence, understanding of EPs is a key to unfold potentials in polariton-based optoelectronics. |
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T00.00248: Exciton Dynamics in Two-Dimensional PTCDA/WS2 Heterojunctions Myeong In Song, Sunmin Ryu Understanding exciton dynamics in two-dimensional (2D) heterojunctions is essential for future applications such as photocatalysis, photosynthesis, and transistors. 2D organic crystals are an ideal model system for studying excitonic behaviors under extreme confinement and reduced dielectric screening. In this work, we report on a confocal transient absorption spectroscopy setup optimized for 2D inorganic and organic semiconductors and interlayer excitonic behavior in their heterojunctions. For a higher sensitivity and flexibility on sample requirements, the change in absorption was obtained in the reflectance mode. The differential reflectance of 140-fs supercontinuum white-light probe beam was measured as a function of the time delay with respect to 100-fs pump pulses (350 ~ 1320 nm). The instrument response function determined by sum frequency generation was ~350 fs, mostly limited by the refractive type microscope objective. For reference, monolayer MoS2 supported on quartz substrates, transient reflectance signals at 660 nm showed a triexponential decay with lifetimes of 0.5, 1.8, and 8 ps, which respectively originate from exciton formation[1], trapping by defect, and carrier scattering[2]. Preliminary data on 2D PTCDA (perylenetetracarboxylic dianhydride) crystals-monolayer WS2 will also be presented. |
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T00.00249: Nanoimprinted pyramid scanning probe for near-field optical mapping Junze Zhou, Edward S Barnard, Adam Schwartzberg, Keiko Munechika, Alexander Weber-Bargioni Scanning near-field optical microscope (SNOM) can simultaneously collect an optical spectrum and topographic information at a spatial resolution beyond the diffraction limit which provides critical insight into understanding how local material properties and structure result in the macroscopic functionality of a material. In the meantime, SNOM enables selective enhancement of the light emission through plasmonic design and nanofabrication on the scanning probe. This work aims at developing a new type of near-field probe using a low-cost and high-throughput nanoimprinting technique for the optical study of low-dimensional quantum materials. The performance of the nanoimprinted probe was demonstrated by high height sensing and high-resolution optical mapping on a 2-dimensional (2D) semiconductor and 0D luminescent nanocrystals. Based on the pyramid probe, we designed and fabricated several near-field configurations for the study of excitonic properties in 2D material including polarization-controlled emission, dark exciton, as well as strong exciton-plasmon coupling. |
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T00.00250: Accelerated neuromorphic computing with site specific joule heating of ECRAM arrays Jillian Anderson Electrochemical random access memory (ECRAM) devices are attractive for their linear, symmetric, and area-scalable switching behavior, useful for artificial synapses in neuromorphic computing. Large scale, network-level reconfigurability of ECRAM has been limited by a lack of knowledge of the underlying thermophysical properties of their constituent materials. Here we use finite-element and numeric simulations with constraints matching typical ECRAM materials to elucidate the electrothermal interactions of ECRAM devices coupled with microheaters. |
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T00.00251: Crystal size determination by comparative methods by X-ray Diffraction in nanocrystalline thin film of Clausthalite and its effect on its photovoltaic properties for applications in solar cells Patricia A Coello, José C Alvarez, ELIZABETH CHAVIRA, Enue B Salgado, Yamilet R Lazcano In the deposition chemical bath synthesis method, the preparation parameters have an important role that determines the final nature of the product formed. There are several factors that affect the structural properties.The variation of the temperature was between 40-60ºC and the range of the time used was between 60 to 240 minutes.The crystal size was estimated by X-ray diffraction. It has been observed that the temperature during the chemical bath deposition is decisive in the optimal morphology properties of the thin film.The crystal size increases as a function of the temperature within an range size of 20 to 30 nm. The band gap does not change significantly with values of 1.06 to 1.1 eV as temperature function.The I-V measurement under dark and bright conditions indicate very low resistance for nanofilms with the optimum temperature (60ºC), optimum time (180-195 min) and thickness values (210-225 nm). The exceptional behavior in the conductivity of (7–11) x10-3W-1cm-1 , makes this material an ideal material for the constructions of a solar cells devices. |
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T00.00252: Investigation of Lead-Free Inorganic Perovskite for Gamma-Ray Detection Applications Charles Han, shea tonkinson, Maya Narayanan Kutty, Adam A Hecht, Ganesh Balakrishnan, Alexander Barzilov Due to the unique crystal structure, the inorganic perovskites such as CsPbBr3 are promising for ambient-temperature radiation detectors. Perovskites have a wide bandgap, high mobility-lifetime product, low defect densities, and long-term stability making these materials promising for radiation detection applications. CsPbBr3, however, has complicated crystal growth conditions such as phase transformations, making it difficult to control the temperature gradient using Bridgman method, and possibly causing degradation of detector performance due to electric defects that disturb photogenerated carriers hopping. The Cs3Bi2I9 (CBI) lead-free perovskite is a candidate for the radiation detector material that allows the control of crystal design with a stable phase transformation stabilizing the crystal structure. In this report, the synthesis of CBI crystals using Bridgman method was studied. The approach utilized computer control of temperature gradient between hot and cold zones, cooling rate, and a vertical translation of the vacuum-sealed quartz tube with the CBI powder. The characteristics of Cs3Bi2I9 crystals will be discussed. The grown crystals were characterized using photoluminescence (room temperature and cryogenic), optical and scanning electron microscopy. We will also provide data on the compositional uniformity via XRD, EDS and SIMS techniques. Electrical characterization of the samples was performed for IV analysis. |
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T00.00253: Understand the Resistive Switching and Reliability Mechanisms of 2D TMD Material: Defect Engineering, Finite Element Analysis and Monte Carlo Modeling Yifu Huang, Yuqian Gu, Xiaohan Wu, Ruijing Ge, Yao-Feng Chang, Ying-Chen Chen, Deji Akinwande, Jack C Lee Two-dimensional (2D) materials become a promising candidate for the resistive random-access memory (memristor) devices. However, reliability is one of the major challenges to the realistic application. We employ an electron irradiation treatment on monolayer MoS2 film to modify the defect properties and improve the reliability. A sulfurization method has been proposed to tune the defect from the beginning of material synthesis. MoS2 memristors are fabricated afterwards. Tuning the sulfurization parameters (temperature/metal precursor thickness) is found to be a simple but effective strategy to improve reliability of memristors. To explain the switching and reliability mechanisms, we proposed the dissociation-diffusion-adsorption (DDA) and cluster model for monolayer 2D MoS2 memristors. Thermoelectric simulations are designed and conducted by COMSOL Multiphysics to demonstrate the Joule heating effect caused by the low resistance regions within the MoS2 layers, which illustrates the mechanism of the RESET. A Monte Carlo (MC) simulator is designed for multilayer 2D memristor to expand the application of DDA and cluster models. The COMSOL simulation results are implemented in the design of resistive switching process in the MC simulator. It is found that the endurance characteristic is mainly determined by the formation and collapsing of an intermediate layer. Also, the thickness of intermediate layer is independent from the total thickness of MoS2 and the initial status of the devices. |
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T00.00254: Poling-driven modulation of structural and luminescent properties in Eu3+-doped (1-x)(Bi1/2Na1/2)TiO3-xBaTiO3 relaxor Yunsang Lee, Sangwon Wi, Jaeho Han, Sang Don Bu We investigated the structural, electric, and luminescent properties of Eu3+-doped (1-x)(Bi1/2Na1/2)TiO3-xBaTiO3 (BNT-xBT:Eu) relaxors for x = 0.0 – 0.08. The Rietveld refinement structural analysis revealed that the structural phase of BNT-xBT:Eu was the mixture of rhombohedral, monoclinic and tetragonal phases with significant x-dependence, which was in accord with the change in the emission spectra originating from Eu3+. Interestingly, we found that BNT-xBT:Eu for x > 0.4 experienced the structural phase transformation on application of electric field. The structural change by poling led to the reduction in the emission of Eu3+. Poling-driven emission quenching behaviors resulted from the increased local structure symmetry around Eu3+ in the poled samples. We also identified the photochromic behavior in our samples, in relation to the doping of Eu3+. These multi-functionality of BNT-xBT:Eu could pave a way to a new type of optoelectric material. |
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T00.00255: Electronic shot noise in the absence of currents: bounds at zero and finite frequency Matteo Acciai, Ludovico Tesser, Christian Spanslatt, Juliette Monsel, Janine SPLETTSTOESSER Nonequilibrium situations where selected currents are suppressed are of interest in fields like thermoelectrics and spintronics, raising the question of how the related noises behave. |
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T00.00256: Are niobium oxide dihalide materials good thermoelectrics: the study case of NbOI2 Bastien F Grosso, David O Scanlon Thermoelectric materials offer the possibility to transform heat waste directly into electrical energy. Finding such materials is challenging since they should have simultaneously a large electrical conductivity and a low lattice thermal conductivity. These almost mutually exclusive conditions are usually encountered in materials containing Pb, making them not sustainable. Therefore, we study oxide dihalide materials as a sustainable alternate option. |
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T00.00257: Simulation study of inelastic neutron-scattering spectra of Si crystals beyond the one-phonon Green's function approximation Jalaan Avritte, David E Crawford, Jianjun Dong Inelastic neutron-scattering (INS) is a powerful experimental probe to study thermal excitations in a vibrating lattice at finite temperatures. Yet, the majority of the current theoretical interpretations of these INS spectra have neglected multiphonon processes by using one-phonon's self-energy evaluated from perturbation theory. We have implemented a robust numeric algorithm to calculate the full scattering spectra based on large-scale molecular dynamics (MD) simulations. Using a silicon machine-learning interatomic potential, we have predicted a set of INS spectra of silicon crystals from 300K to 1500K. We demonstrate that a q-space symmetrization technique significantly reduces intrinsic numeric uncertainties associated with the MD simulations of thousands of atoms over hundreds of picoseconds. Our simulated temperature-dependent INS data are in excellent agreement with recent phonon dispersion curves. In addition, our data reveals many spectra details that are not yet observable even in the state-of-the-art experiment. Furthermore, we quantitatively analyze the individual contributions due to single-phonon processes, multiple phonon processes, and interference between the single phonon and multiple phonon processes, using a decomposition algorithm. We will discuss the temperature-dependent line shapes of the phonon peaks in the INS spectra and the implications for phonon lifetime calculations at high temperatures. |
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T00.00258: Formation of Self-Trapped Holes in Silica From Density Functional Theory David D Dai, Ali Ghorashi, Marin Soljacic Self-trapped holes (STHs) are defects formed in silica when holes couple with phonons and localize. They play a crucial role in understanding silica's interaction with light in applications such as scintillators and optical fibers. Ab-initio studies of STHs through DFT have been performed and benchmarked against experimental data, but they considered only the final polaron and not its formation process. Additionally, the results were sensitive to the fraction of exact exchange used. In this work, we compute the Eliashberg spectral function and electron-phonon matrix elements to provide a more detailed description of STH formation, and we use Koopman's theorem to tune the amount of exact exchange to include, correcting both deficiencies with earlier studies. Our approach enables us to rationalize why certain types of STHs, differentiated by their geometry, are available in amorphous vs crystalline silica. Furthermore, we find that the phonon modes most strongly coupled to the hole are those similar to the final lattice distortion in the polaron. Overall, our approach for more accurate description of STHs may enable the development of better devices as well as motivate future ab-initio exploration of STHs. |
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T00.00259: Exchange and Correlation Effects on the Spin and Charge Susceptibilities of Tilted 1T′ MoS2 SITA KANDEL The exchange and correlation energies due to the Coulomb interactions in monolayer tilted 1T′MoS2 are calculated. We use the Lindhard formalism for the polarizability propagator. Many- body effects in such Dirac-like materials are studied with an emphasis on the influence of the mis- alignment of the conduction and valence subbands. Our calculations have shown that the presence of an energy band gap leads to a reduced exchange energy, which has some potential applications, such as, tunability of exciton polariton and plasmon excitations. Since 1T′MoS2 acquires two energy gaps associated with up- and down- pseudospin, we can adjust its electronic properties in a wider range by varying these two band gaps in contrast with graphene. |
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T00.00260: Ab-Initio Computations of Electronic and Related Properties of Cubic Magnesium Silicide (Mg2Si) YURIY MALOZOVSKY, Dioum Alle, Yacouba Issa Diakite, Blaise Awola Ayirizia, Aboubaker Chedikh Beye, Diola Bagayoko We have performed ab-initio, self-consistent calculations of electronic, transport, and bulk properties of cubic magnesium silicide (Mg2Si). Our computations employed the local density approximation (LDA) potential of Ceperley and Alder and the linear combination of atomic orbital (LCAO) formalism. We performed a generalized minimization of the energy using successive, self-consistent calculations with augmented basis sets to reach the ground state of the material, y, without employing over-complete basis sets. For a room temperature lattice constant of 6.338 Å, our calculated, indirect band gap, from Γ to X, is 0.896 eV. We discuss the total and partial densities of states, electron and hole effective masses, and the bulk modulus. Our calculated bulk modulus of 58.58 GPa is in excellent agreement with experimental value of 57.3 ± 2 GPa. Our predicted equilibrium lattice constant and band gap, at zero temperature, are 6.218 Å and 0.965 eV. |
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T00.00261: Core/shell nanowire heterostructures as efficient nanoscale photon upconverters Irina A Buyanova, Mattias Jansson, Fumitaro Ishikawa, Weimin M Chen Photon energy upconversion in semiconductor nanowires (NWs) could be utilized in a verity of nano- optoelectronic and photonic applications. In this work we show that efficiency of energy upconversion due to two-photon absorption (TPA) can be boosted in NW heterostructures engineered so that (i) an intermediate TPA step involves band states of the narrow bandgap region; (ii) at least one of the carriers created after the first photon absorption can freely diffuse to the wider bandgap region; and (iii) carriers generated after the intermediate step have a long lifetime. These conditions are shown to be satisfied in radial GaNAs(P)/GaAs(P) NW heterostructures leading to up to 500 times increase in the upconversion efficiency relative to that of the constituent materials. The upconversion efficiency is found to be independent of the excitation power and can be further enhanced (up to 15%) in hybrid NW-on-gold structures, engineered to maximize light absorption within the shell region under the upconversion conditions. This work, therefore, demonstrates the great potential of dilute nitride NWs as energy upconverters and provides general guidelines for designing efficient nanoscale photon upconverters based on NW heterostructures. |
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T00.00262: Role of magnetic field on the variation of specific heat capacity of graphene. Dipendra Dahal Using Green's function approach, we have carried out the calculation of the specific heat capacity for graphene in the presence of the magnetic field. Strong and weak magnetic field splits the energy level of graphene into different Landau level whose density of state are well evaluated and presented graphically as a function of magnetic field and also energy eigenvalues. making use of this density of state, both theoretical and numerical evaluation of specific heat capacity is done. A fluctuating heat capacity with the rise in temperature is obtained for various strengths of the magnetic field. In addition, the applications of specific heat capacity knowledge in designing heat memory devices are discussed. |
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T00.00263: Temperature Dependent Photoluminescence Studies of Mn Doped ITO Thin Films Masoud Kaveh Transparent conducting oxides (TCOs) have attracted a lot of attention in recent years due to their vast applications in flat panel displays, LEDs, solar cells, and wearable electronics. TCOs are electrically conductive, and their large energy band gap makes them optically transparent. Such versatile materials could potentially be used in spintronic devices if some degree of ferromagnetism can be achieved. In this study we optically investigate the effects of manganese doping on the energy band structure of Indium Tin Oxide (ITO), a widely used TCO. Thin films of ITO doped with various Mn concentrations are deposited on quartz substrates by DC magnetron sputtering. We then use low temperature photoluminescence (PL), transmission measurements, ellipsometry, and x-ray diffraction to characterize these films. The PL measurements reveal blue and UVA emission peaks. The blue emission is also consistent with blue absorption bands from our ellipsometry measurements, and it is tentatively attributed to the indirect bandgap of ITO. The PL intensity decreases with increasing Mn concentration which is attributed to upward shift of the valence band. Temperature dependent PL measurements show a decrease in the PL intensity and a red shift of the blue peak with increasing temperature. To our knowledge, these are the first temperature dependent optical studies of Mn doped ITO samples. |
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T00.00264: A feasible experimental synthesis of a new aluminum nitride polytype in view of the DFT calculation Se-Hun Kim We present the results of a first-principles study on the structural stability and electronic and optical properties of new aluminum nitride (AlN) polytypes. The study includes the following experimentally or theoretically known phases of AlN: wurtzite (WZ), zincblende (ZB), and rocksalt (RS) structures, which complement the pressure-dependent phase diagram of this industrially important compound. In addition to the structures of AlN considered in previous studies, we evaluated the dynamical stability of various novel phases, viz., SiC(4H), ZnS(15R), BeO, 5-5, TiAs, NiAs, MoC, Li2O2, and NiS. These were predicted recently in a high-pressure data mining study of more than 140,000 variations of the AlN structure, which claimed that they were either stable or nearly stable, based on first-principles calculations. Based on the new AlN polytypes, the physical properties of all considered phases were compared, and the common trends and differences were determined. According to the phonon band structure calculations, nine phases of these new polytypes are free from imaginary frequencies. This indicates adequate dynamical stability, and experimental accessibility of the polytypes. Additionally, the calculated cohesive energies of the dynamically stable phases are comparable to those of WZ-AlN and those specified in the available literature. Furthermore, the observed electronic structures and optical properties indicate that the polytypism of AlN can be a practical tool for refining its physical and chemical properties. The new phases show significant potential for use in future electronic and optoelectronic applications of AlN. |
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T00.00265: Temperature-dependent infrared spectrum of NbxV1-xO2 single crystals at the phase transition Yejin Kwon, Top B Rawot Chhetri, Zachary Brown, Wade DeGottardi, Jared M Allred, Myoung-Hwan Kim Vanadium dioxide (VO2) is famous for the reversible metal-to-insulator transition - from an insulating monoclinic phase to a metallic rutile phase - slightly above room temperature which allows many photonics applications such as optical switching and modulators. Since the metal-to-insulator transition temperature is sensitive to the concentration of substituents, lower or higher the transition temperature by doping chemical substitution expands VO2 application to the lower energy scale. Here, we investigate an optical property of NbxV1-xO2 single crystals (x = 0.4, 0.11, 0.15, 0.24, 0.35, and 0.88) across the metal-to-insulator transition. Although VO2 and NbO2 are isoelectronic and show the same type of metal-to-insulator transition, the transition temperature of NbO2 is much higher than that of VO2. NbxV1-xO2 alloy will help in resolving the structural and electronic connection among crystal phases. We measured a broadband reflection spectrum from visible to long-wave mid-infrared at various low temperatures. We obtained an optical conductivity of NbxV1-xO2 extracted by using Kramers-Kronig analysis. To evaluate the metal-to-insulator or the metal-to-semiconductor transition, we applied an extended Drude model to fit the optical conductivity. |
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T00.00266: Substitutional doping defects in two-dimensional GaSe as potential single-photon emitters Rumana Zahir, Sergey Stolbov Single-photon emitters (SPE) have attracted enormous attention because they are essential components of emerging quantum communication technology. The emission in the near-infrared (NIR) range is of special interest for fiber-based applications. In this work, we consider the substitution defects in GaSe as potential sources of such emission. We selected the XSe and XGa defects where X = C, Si, Ge, N, P, and As (we use the common XY notation where X is the dopant and Y is the substituted atom). We first evaluated the stability of the defects by analyzing the defect formation energies and phonon spectra obtained through density functional theory-based calculations. After identifying the stable defects, we calculated their optical excitation spectra using the linear response GW and the Bethe-Salpeter equation (BSE) methods. We found that the defects such as CSe, NSe, SiSe have sharp intense excitation peaks in the region of 0.8 - 1.5 eV. The analysis of the contributions of the independent quasiparticle states (eigenstates of GW) to the corresponding BSE eigenstates suggests that these excitations can result in the emission with dominating narrow zero-phonon lines accompanied with the low-intense and narrow phonon sidebands. We thus propose the defects to be promising SPEs in NIR range. |
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T00.00267: The impact of asperity shape and gradient elasticity in flexoelectric/triboelectric contacts Karl P Olson Flexoelectricity, the coupling of strain gradients and polarization, is necessary to explain the charge transfer that occurs when an insulator contacts another material, known as triboelectricity. When asperities at the surface of materials contact, they deform with a large strain gradient, which drives charge transfer via the flexoelectric effect [1]. Previously, we have developed an experimentally verified model for metal-semiconductor contacts which explains the force-dependence of current when an atomic force microscope tip is used to deform the semiconductor [2]. |
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T00.00268: Electrical transport and photoconductivity in pulsed dc sputtered WSe2 thin film* Ravinder Kumar, Jyotsna Das, Ahamed Raihan, Ramesh C Budhani, Dereje Seifu 2D-layered materials exhibiting interesting electronic transport are potential candidates for the field of spintronics [1]. We report thin film growth of transition metal dichalcogenide (TMD) WSe2 using the pulsed dc sputtering technique. The electronic transport properties of Hall patterned WSe2 thin films are studied as a function of temperature and magnetic field. The sample shows semiconducting behaviour with holes as a majority charge carrier. We use interdigitated electrodes to measure the photo-response of WSe2 film by using infrared, green and blue lasers. The gate-tuning of the photo-response is also observed to realize WSe2-based phototransistor. Our study may have strong implications in the development of the field of 2D TMD-based devices. |
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T00.00269: Impedance Analysis of the Morphology Dependence of the Dielectric Properties of Four Different ZnO Nanomaterials Grant M Mayberry, Rusiri E Rathnasekara, Parameswar Hari ZnO nanostructures are an important semiconductor for third-generation photovoltaic (PV) cells as well as other electronic devices. In this study, we report results from impedance spectroscopy measurements on four ZnO morphologies - in order of increasing spherical symmetry and decreasing surface roughness: nanoribbons (NRIs, ~10µm), nanorods (NROs, ~7µm), nanoshuttles (NSs, ~1µm), and nanoparticles (NPs, ~20nm) - to determine the relationship between morphology and dielectric response. The nanostructures are prepared by chemical bath deposition. NRIs, NROs, and NSs are prepared and measured on FTO glass slides, which makes the data from the study ideal for PV applications. Scanning Electron Microscopy and Tunneling Electron Microscopy were used to measure the dimensions of these four morphologies. Impedance spectra in the 100Hz-5.1MHz frequency range suggest that decreasing complexities of surface structures and increasing spherical symmetry leads to an increased dielectric constant of ZnO nanostructures at low frequencies. This increased dielectric constant is also clearly manifested in the phase spectra of each morphology from 100Hz-10kHz. |
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T00.00270: Material characterization of polymer controlled solution grown single crystal hybrid perovskites MAPbBr3 and FAPbBr3 for detectors of ionizing radiation Kaleab Ayalew, Jaeyun Moon, shea tonkinson, Maya Narayanan Kutty, Adam A Hecht, Ganesh Balakrishnan, Alexander Barzilov Detectors of ionizing radiation require materials with strong stopping power, low defect concentration, wide bandgap, and excellent charge mobility. Single crystal organic-inorganic perovskites (ScOIHP) have attracted recent attention as a potential detector material. Wide utilization of ScOIHP for radiation detection calls for efficient and low-cost crystal growth techniques. Here we report high-quality CH3NH3PbBr3 (MAPbBr3) and CH(NH2)2PbBr3 (FAPbBr3) single crystals grown using a polymer-controlled solution method. An extensive material characterization on the as-grown single crystals are presented including the crystal’s quality and semiconductor properties. Process improvement avenues are discussed by comparing properties of the as-grown ScOIHP with the state-of-the-art detector materials. The grown crystals are characterized for a variety of parameters using photoluminescence (room temperature and cryogenic), optical microscopy, and scanning electron microscopy. We will also provide data on the compositional uniformity via XRD, EDS and SIMS techniques. Electrical characterization of the samples is performed for IV analysis. |
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T00.00271: High-Performance Junction-Free Field-Effect Transistor Based on Blue Phosphorene Udo Schwingenschlogl, Paresh C Rout, Shubham Tyagi Two-dimensional semiconductors have great potential in high-performance electronic devices. However, the common way of contacting them with metals to inject charge carriers results in contact resistance (leading to poor current delivering capability) and remains a bottleneck in the scaling of modern devices. We will discuss a junction-free field-effect transistor consisting of semiconducting monolayer blue phosphorene as channel material (with high carrier mobility) and metallic bilayer blue phosphorene as electrodes. The junction-free design minimizes contact resistance. Employing first-principles calculations along with the non-equilibrium Green’s function method, we demonstrate an ultra-low contact resistance, a high Ion/Ioff ratio of up to 2.6×104 and a remarkable transconductance of up to 811 μS/μm. |
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T00.00272: INDUSTRIAL AND APPLIED PHYSICS
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T00.00273: A Design Methodology for Fault-Tolerant Computing Using Astrocyte Neural Networks Murat Isik We propose a design methodology to facilitate fault tolerance of deep learning models. First, we implement a many-core fault-tolerant neuromorphic hardware design, where neuron and synapse circuitries in each neuromorphic core are enclosed with astrocyte circuitries, the star-shaped glial cells of the brain that facilitate self-repair by restoring the spike firing frequency of a failed neuron using a closed-loop retrograde feedback signal. Next, we introduce astrocytes in a deep-learning model to achieve the required degree of tolerance to hardware faults. Finally, we use a system software to partition the astrocyte-enabled model into clusters and implement them on the proposed fault-tolerant neuromorphic design. We evaluate this design methodology using seven deep-learning inference models and show that it is both area- and power-efficient |
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T00.00274: Giant photo-amplification in air-stable α-CsPbI3 nanocrystals / WS2 0D / 2D mixed-dimensional phototransistor with asymmetric contacts Shreyasi Das, Arup Ghorai, Sourabh Pal, Somnath Mahato, Soumen Das, Samit K Ray Hybrid heterostructures comprising of 2D transition metal dichalcogenides (TMDs) and 0D perovskite nanocrystals having excellent photosensitive characteristics offer the possibility to achieve next generation optoelectronic devices with superior functionalities. However, the absence of any in-plane built-in electric field in these single channel layer transistors results in relatively higher dark current and a larger gate voltage is necessary to deplete the channel. To overcome these limitations, air stable Cesium lead iodide/Tungsten di-sulfied (CsPbI3/WS2) mixed dimensional heterostructure based phototransistors are reported with asymmetric metal electrodes (Cr/WS2/Au), exhibiting extremely low dark current (~10-12 A) with a high responsivity (~ 102 A/W) at zero gate bias. In these devices, the Schottky barrier at WS2/Au interface accompanied with excellent photoabsorbing attributes of solution-processed α-phase CsPbI3 sensitizers, result in gate-tunable broadband phototransistor with high responsivity (~104 A/W). Most interestingly, the device shows superior performance even under high humidity (50-65%) conditions owing to the formation of cubic α-phase CsPbI3 with a relatively smaller lattice constant (a = 6.2315 Å). These outcomes highlight a novel strategy to utilize the metal semiconductor Schottky junction in combination with photosensitive perovskite NCs decorated TMD based hybrid heterostructures for developing large-scale optoelectronic devices. |
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T00.00275: Non-thermal plasma and catalyst system for indoor VOC removal Suhan Kim, Wellawatta W Thusitha Indoor air quality control has received a lot of attention in recent years. Since clean indoor air cannot be secured by ventilation alone, the development of air purification technology is being actively carried out. |
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T00.00276: Robust Higher Harmonic Generation at Exceptional Points Amir Targholizadeh, Hamidreza Ramezani, Cem Yuce, Gui-Lei Zhu, Xin-yu Lu Harmonic generation occurs in driven systems including electronics, acoustics, and photonics. In the frequency conversion process geometrical defects of the medium can alter the coupling between the fundamental frequency and the Second Harmonic and thus it plays a significant role in the phase, and amplitude of the converted frequency. This dependency to the geometrical properties creates a barrier in making precise devices such as upconverted coupled lasers and antenna remoting applications to name a few. Here, we propose a new method to robust Second Harmonic Generation using a class of topological singularities that occurs in non-Hermitian-driven systems which is totally different from Nonlinear Harmonic Generation using kai(2) materials. Specifically, we propose a complex spatiotemporal susceptibility modulation in a slab silicon waveguide. We show the frequency conversion process in such modulated system is governed by a non-Hermitian Hamiltonian. By choosing a equivalent amplitude for real and imaginary part of the modulation, fundamental mode becomes decouple from Second Harmonic which can create a Jordan From Hamiltonian operating at the exceptional point which is independent of geometrical imperfection. |
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T00.00277: Electronic Nose based on MOS Nanowires Gas Sensor Array for Breath Analysis Application Chuanlai Zang, Hitoshi Tabata, Hiroyasu Yamahara Inspired by the mammalian olfactory system, artificial olfactory (also known as electronic nose) have been developed based on cross-reactive sensor arrays that interact differentially with target molecules to generate a fingerprint pattern recognition which is realized by artificial intelligent technology. Oxide semiconductor chemical gas sensors have many irreplaceable advantages, such as high and unique response to various gases, reversibility, simple structure, silicon compatibility, easy miniaturization and cost-effectiveness. They are an excellent platform for realizing complex and integrated artificial olfaction. This work applies a facile electrospinning method and electrode beam lithography method to develop the four different metal oxide semiconductor (MOS) nanowires sensor array. The dynamic sensing response of the fabricated multiple nanofibers sensor array was measured for human breath. The time serial resistance of each sensor was recorded. Considering that gas sensors with different oxide materials have different responses to kinds of gas molecules, their characteristics are calculated through the obtained time series resistance change curve, including resistance change, response, and recovery time. The breath analysis demonstration video clearly shows that when the fabricated sensor is exposed to human breath, the voltage suddenly decreases, indicating that the resistance of the fabricated gas sensor decreases. It shows the possibility of applying gas sensors in breath analysis to identify the VOCs in the exhaled human breath. The practical applications of gas sensors are determined by their sensitivity, stability, and selectivity. However, it is unclear whether the fabricated gas sensor can produce a stable response to tiny changes in the gas concentration, as well as whether the sensor array can specifically identify different gas components. These aspects should be studied in detail in the future. |
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T00.00278: Strain Driven Anomalous Anisotropic Enhancement in the Thermoelectric Performance of Monolayer MoS2 Saumen Chaudhuri, Amrita Bhattacharya, Amal K Das, Gour P Das, Bhupendra N Dev The anisotropic tuning of the transport and thermoelectric properties of monolayer MoS2 with the application of in-plane tensile strains along the armchair (AC) and the zigzag (ZZ) direction have been explored based on first-principles calculations. Tensile strain, in general, is found to have a diminishing effect on the thermopower and power factor of monolayer MoS2, with greater impact on the p-type carriers. However, considering the intrinsic carrier-phonon scattering, we found that the charge carrier mobility (µ) and relaxation time (τ) increases remarkably for strains along the ZZ direction. Concomitantly, strain along the ZZ direction significantly reduces the lattice thermal conductivity (κL) of ML-MoS2. The combined effect of shortened phonon relaxation time and group velocity, and the reduced Debye temperature is found to be the driving force behind the lowering of κL. The large reduction in κL and increase in τ, associated with the strains along the ZZ direction, acts in unison to result in an enhanced efficiency and hence, improved thermoelectric performance throughout the temperature range of 200K to 900K. Nearly 150% enhancement in the thermoelectric efficiency can be achieved with the optimal doping concentration. We, therefore, highlight the significance of in-plane tensile strains, in general and strains along the ZZ direction, in particular, in improving the thermoelectric performance of ML-MoS2, which could open avenues for its application in emerging areas of 2D-thermoelectrics. |
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T00.00279: Applications of Optically Pumped Magnetometers in Fundamental Physics and Biophysics Young Jin Kim, Igor M Savukov Optically Pumped Magnetometers (OPMs) are based on alkali-metal vapor cells and lasers to manipulate atomic spins for magnetic sensing and are currently the most sensitive non-cryogenic magnetic-field sensor reaching femtoTesla sensitivity. Over the years we have used OPMs for some novel applications in fundamental physics and biophysics. In this talk, we will give an overview of the applications and present recent results. For example, we have developed new detection concepts based on OPMs to search for new fundamental bosonic particles, such as axions. Also, we have designed and constructed a single-module multichannel OPM for accelerated biomagnetic imaging, such as magneto-encephalography and magnetic resonance imaging. |
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T00.00280: Green Bismuth based upconversion material for bioimaging of cells Manisha Bungla, Ashok K Ganguli Upconversion materials have attracted considerable research interest for their application in bioimaging due to their unique optical properties. Host lattice which are been widely used for upconversion, requires expensive rare-earth elements and tedious reaction conditions. Hence there is a need to develop environmental friendly and cost effective materials for upconversion. In this study, we propose NaBiF4 as a host material for upconversion which is based on environmental friendly and cost effective bismuth. NaBiF4 has not been explored as imaging probes earlier. Here, we functionally validate these nanoparticles as viable alternatives to the currently available upconversion nanomaterials and highlight their potential as luminescent nanoprobes for bioimaging. |
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T00.00281: Shape-Morphing Tissue Engineering Scaffolds Based on Hydro-thermal Responsive Polymers Xiaodie Chen, Jiahui Lai, Liwu Zheng, Min Wang Shape-morphing tissue engineering scaffolds attract increasing attention as they can meet the demanding requirements of some clinical applications and adapt to local body environments. 4D printing is a suitable tool for fabricating such scaffolds with the use of shape memory polymers (SMP). But most SMPs can only respond to a single stimulus, while the human body can provide multiple stimuli. Blending a synthetic SMP with a biocompatible natural hydrogel that can respond to other stimuli can produce a material with good shape memory capability and desirable biological properties. In this study, poly(D,L-lactide-co-trimethylene carbonate) (PDLLA-co-TMC)/gelatin methacryloyl (GelMA) blends were made and 4D printed into scaffolds that have desired properties and can respond to hydro-thermal dual stimuli. The morphology, chemical composition, structure and mechanical properties of fabricated scaffolds were investigated. Their shape morphing behaviour was studied at 37 ? in air and in water. PDLLA-co-TMC/GelMA blend scaffolds showed good biocompatibility and much improved mechanical properties. In vitro degradation of PDLLA-co-TMC/GelMA scaffolds was significantly faster. For dynamic shape changes from flat to circular shape, they could respond to hydro-stimulus, which was achieved via depth-changing UV irradiation of scaffolds, and thermal-stimulus due to PDLLA-co-TMC. These shape-morphing scaffolds have the potential for regenerating tubular tissues such as blood vessels. |
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T00.00282: Polymer Shell Liquid Core Nanocapsules Synthesized by Flash Nanoprecipitation for Biomedical Applications Yuri Chung With advances in the development of nanoparticles, interest in multicomponent materials has grown. |
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T00.00283: Selective detection of uric acid through MoS2 modified paper sensor: experimental validation of ab-initio estimations Arijit Pal, Souvik Biswas, Koel Chaudhury, Soumen Das Selective estimation of uric acid in different biofluids is an open research problem as it has a similar oxidation potential compared to ascorbic acid. The present study involves MoS2-modified paper substrate as a sensing platform to detect uric acid distinctively. A single-step hydrothermal method was employed to grow MoS2 micro flower over the paper substrate. The modified paper substrate was characterized with FESEM, XRD and Raman Spectroscopy to validate the proper formation of MoS2 microflowers. These MoS2-modified paper sensors were further used to determine different uric acid concentrations through a non-enzymatic approach where oxidation of uric acid occurs at the surface of the sensing region. To promote the suitability of MoS2 towards selective detection of uric acid, an extensive first principle calculation has been carried out by inserting different biomolecules i.e. uric acid, ascorbic acid, and dopamine inside the unit cell of 2H-MoS2. The obtained electronic band gap and projected density of states analysis confirm the selectivity of the MoS2 towards uric acid detection. Different electrochemical measurements like cyclic voltammetry and differential pulse voltammetry were employed to verify the change in oxidation potential of uric acid in presence of MoS2-modified paper substrate. These experimental findings can also be corroborated by the charge redistribution of uric aid adsorbed MoS2 structure obtained through Löwdin population analysis. |
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T00.00284: SHOCK COMPRESSION OF CONDENSED MATTER
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T00.00285: Enhanced Impact Resistance of Bouligand Films with Discontinuous Cellulose Nanocrystal Nanofibers Colby D Caviness, Zhaoxu Meng, Zhangke Yang, Haoyu Wang Significant knowledge gaps exist in the understanding of the dynamic mechanical behaviors of thin films consisting of discontinuous nanofibers with a Bouligand microstructure. In this study, we applied coarse-grained molecular dynamics simulations to investigate the impact resistance of Bouligand microstructural films with integrated defects, i.e., aligned but discontinuous cellulose nanocrystal nanofibers. Through explicit projectile impact simulations, we have investigated the impact resistance of Bouligand CNC films depending on different variables, such as defect types, fiber length (or defect density), and pitch angle. Typical ballistic impact indicators, e.g., ballistic limit velocity and penetration energy, were adopted to analyze the impact resistance. We find that defects within the discontinuous microstructure for certain fiber lengths and pitch angles can allow for better performance than continuous counterparts in impact resistance. This study fosters a deeper understanding of the dynamic mechanical behaviors of thin films with the Bouligand microstructure and potential methods to enhance the impact resistance of such films. |
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T00.00286: Testing for Universal Characteristics in the Melting/Freezing Transition of Sn Reetam Paul, Stanimir Bonev, Christine J Wu Much of the theoretical discussion on melting of crystalline solids focuses on the usage of methods which employ free energy matching or direct molecular dynamics simulations of phase transitions, such as heat-until-melt, Z-method or two-phase coexistence-based simulations. In this work, we examine the melt/freeze signatures in Sn not just by using the aforementioned techniques, but also by putting to test the approach developed by Daligault [1]. It proposes the existence of a universal structural metric defined on the basis of the mean first-passage time of atomic motion in a liquid phase and devoid of explicit thermodynamic considerations, which is sufficient to accurately predict the onset of freezing transition in monoatomic liquids. |
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T00.00287: Investigation of Dynamic Impact Response of PMMA-Graphene Layered Nanocomposite Films Using Molecular Dynamics Simulations Zhangke Yang Polymer nanocomposite films show superior energy dissipation capability with the advancement of the micro-projectile impact testing method. However, the detailed stress wave propagation and dynamics failure mechanisms during the extreme rate impact loading process have remained elusive. We will report our recent effort to understand these mechanisms through the lens of molecular dynamics (MD) simulations. We have constructed representative layered nanocomposites consisting of PMMA and graphene phases by using their corresponding coarse-grained models and applied MD simulations to study their dynamic impact responses. A piston impact process has been simulated. By analyzing the spatiotemporal distribution of tensile stress and cross-section density, we find that the internal interfaces between graphene and PMMA can reflect, redirect, and attenuate the stress waves. Our results also indicate that the interfacial energy between PMMA and graphene plays an important role in the energy dissipation process, especially with densely distributed graphene layers. Our study provides insights into the design of nanocomposite films with excellent impact resistance through the configuration and distribution of the rigid nanofillers in a soft matrix and their interfacial interactions. |
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T00.00288: Magnetic and electronic properties of EuMnSb2 under high pressure Raimundas Sereika, Zachary Nix, Rongying Jin, William A Shelton, Weiwei Xie, Jiyong Zhao, Esen E Alp, Barbara Lavina, Yuming Xiao, Dongzhou Zhang, Jingui Xu, Yogesh K Vohra, Wenli Bi EuMnSb2 is a magnetic topological Dirac semimetal candidate with large magnetoresistive behavior and exceptional electronic transport properties. The strong coupling of Eu moment with the charge transport offers a potential pathway to control topological properties. In this work, we have investigated the pressure tuning of magnetism, valence states, and crystal structure. Time-domain synchrotron Mössbauer experiments in 151Eu have been performed on EuMnSb2 under quasihydrostatic pressure to investigate the evolution of local moment from the Eu sublattice. High-pressure angular-dispersive X-ray diffraction experiments were conducted to probe the change in crystal structure while X-ray absorption near edge structure experiments performed at Eu’s L3-edge and Mn’s K-edge were used to examine valence states of Eu and Mn, respectively. We have documented remarkable changes in the magnetic properties and valence states under high pressure. The mechanism of these changes and their relation to the crystal structure will be discussed in detail. |
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T00.00289: New design for high static pre-compression in shock dynamic experiments Anand P Dwivedi, Sylvain Petitgirard, Karen Appel, Erik Brambrink, Konstantin Glazyrin, Rachel Husband, Zuzana Konôpková, Marius Millot, Thomas Preston, Alessandra Ravasio, Cornelius Strohm, Ulf Zastrau, Valerio Cerantola We introduce a new shock diamond anvil cell (SDAC) design for combining high static pre-compression and sub-kJ laser-driven dynamic shock compression experiments at X-ray sources. We designed a system of two thin diamond anvils, one of which is perforated with a thin diamond window (30-70 μm) glued on top of the culet. The perforation is envisioned to allow shock waves created by low/moderate energy lasers to propagate through the sample. Being developed to be usable by any user community at the High Energy Density (HED) instrument at European-XFEL, or other large-scale facilities around the world, the unique design of the SDAC will allow reaching higher density states of matter in shock compression experiments and probe previously unexplored regions of the pressure-temperature-density phase diagram, combined with the diagnostics capability of the XFEL. We will present the results of our technical development, hydrodynamic, and potentially molecular dynamics simulation results of dense Krypton, laser-shocked at different initial densities. |
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T00.00290: DATA SCIENCE
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T00.00291: Machine Learning Assisted Prediction of Physical Properties of Cyclotides Sairam Tangirala, Rachel Schaffer, Ajay Mallia, Simon Mwongela, Neville Forlemu Cyclotides are organic molecules that typically contain 28-37 amino acids. They may be isolated from certain plants and have a wide range of biological activity such as being insecticidal, anti-tumor, anti-microbial. Their biological activity and remarkable chemical stability provide an exciting range of potential therapeutic applications. Traditional Molecular Dynamics (MD) studies of cyclotides experience computational limitations due to the large number of atoms in cyclotides. Machine-learning models serve as cost-effective and time-saving computational tools in predicting their physical properties which may be compared to MD calculations. |
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T00.00292: Machine learning and quantum-guided modeling of metal oxide thermodynamic properties Vahe Gharakhanyan, Jose A Garrido Torres, Nongnuch Artrith, Alexander Urban Investigating and optimizing processes at high temperatures is experimentally challenging, and first principles modeling is computationally demanding and typically too approximate. |
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T00.00293: Machine Learning Prediction of Perovskite Solar Cell Propertiesunder High Pressure Minkyung Han, Chunjing Jia, Yu Lin, Cheng Peng, Feng Ke, Youssef Nashed Halide perovskites are promising solar cell materials due to their suitable bandgap range and high tunability. However, materials based on the organic-inorganic (MA)PbI3 (MA = CH3NH3+) suffer a chemical instability issue to heat and moisture due to the volatile MA cation, while the all-inorganic Cs-based analogs present a phase instability challenge where the functional perovskite phases are unstable at ambient conditions and spontaneously convert into the thermodynamically stable non-perovskite phase. Therefore, stabilizing the perovskite phases at room conditions is crucial to achieving higher efficiency and commercialization. Tuning the structure by applying pressure and strain is an effective way to modify the stability and electrical properties of perovskite phases. In this work, we investigate the leading structural features that determine the material properties of the perovskites upon compression. We use various machine learning models to train the large-scale dataset obtained from first-principles DFT calculations. This study will provide insights into developing general models to predict the relationship between structural and electrical properties of similar perovskite structures using cost-effective machine learning approaches. |
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T00.00294: Mesh-agnostic PDE Operator Learning with Attention Zijie Li, Kazem Meidani, Amir Barati Farimani Data-driven learning of partial differential equations' solution operators has recently emerged as a promising paradigm for approximating the underlying solutions. The solution operators are usually parameterized by deep learning models that are built upon problem-specific inductive biases. An example is a convolutional or a graph neural network that exploits the local grid structure where functions' values are sampled. The attention mechanism, on the other hand, provides a flexible way to implicitly exploit the patterns within inputs, and furthermore, relationship between arbitrary query locations and inputs. In this work, we present an attention-based framework for data-driven operator learning, which we term Operator Transformer (OFormer). Our framework is built upon self-attention, cross-attention, and a set of point-wise multilayer perceptrons (MLPs), and thus it makes few assumptions on the sampling pattern of the input function or query locations. We show that the proposed framework is competitive on standard PDE benchmark problems and can flexibly be adapted to different types of grids. |
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T00.00295: Protein Secondary Structure Composition from a Single Unassigned 1D 13C NMR Spectrum Haote Li The characterization of protein structures underpins our understanding of protein function. A wide range of spectroscopic and computational tools have been developed to predict, classify, and characterize protein secondary structure. Here, we introduce an automated gradient descent-based method we refer to as Secondary Structure Distribution by NMR that allows for rapid quantification of the protein secondary structure composition of a protein from a single, 1D 13C NMR spectrum without chemical shift assignments. The analysis of nearly 900 proteins with known structure and chemical shifts demonstrates the capabilities of our approach. We show that these results rival alternative techniques such as FT-IR and circular dichroism that are commonly used to estimate secondary structure compositions. The resulting method requires only the primary sequence of the protein and its referenced 13C NMR spectrum. Each residue is modeled in an ensemble of secondary structures with percentage contributions from random coil, α-helix, and β-sheet secondary structures obtained by minimizing the difference between a simulated and experimental 1D 13C NMR spectrum. The capabilities of the method are further demonstrated as applied to samples at natural abundance, including data acquired by either solution or solid-state NMR. This approach allows for rapid characterization of protein secondary structure across traditionally challenging to characterize states including liquid-liquid phase-separated, membrane-bound, or aggregated states. |
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T00.00296: Using ML techniques to discriminate the tHq(b ¯b) decay channel signal from background Arthur Alves Machine Learning techniques are of very importance when analyzing large amounts of data as the ones acquired by the ATLAS detector. This project focus on the employment of Graph Convolutional Networks (GCN) together with the Deep Graph Library (DGL) to discriminate the signal of the production of a Higgs boson and a single-top quark in the tHq(b ¯b) channel . Python scripts were written to create the graphs and to train and test the Neural Networks. The main goal of using DGL to create the GCN was achieved, however several parameters still have to be altered in order to get a higher test accuracy. |
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T00.00297: Machine Learning for Improvements to Gamma Spectroscopy in Nuclear Fusion Diagnostics Kimberley S Lennon, Callum Grove, Joseph Neilson, Chantal Nobs, Lee Packer, Robin Smith Fusion diagnostics are critical on the path to commercial fusion reactors, since the ability to understand and measure plasma features is important to sustaining fusion reactions. Gamma spectroscopy is one technique used to aid fusion diagnostics, to provide information on ion distribution and also in neutron activation analysis to calculate fusion power. However, a common feature with gamma spectroscopy is Compton scattering events within the detector. These elevate the background, reducing the likelihood of detecting peaks from low-energy gamma rays, leading to higher detection and characterisation limitations. |
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T00.00298: Nanoplasmonic waveguide design driven by multilayer perceptron artificial neural network algorithm Jingcheng F Ma, Yujie Wang, Kaveh Delfanazari Deep learning has gained growing popularity in multiple research fields by utilizing algorithms and statistical models to reveal underlying patterns of data that are collected from a problem, as distinct from its tedious mathematical calculation-related or time-consuming simulation counterparts. In this work, we apply a data-driven approach to the analyses of two nanoplasmonic waveguides, namely the Conductor-Gap-Dielectric (CGD) model and the Conductor-Gap-Conductor-Dielectric (CGCD) model. We first collect data from these two models via COMSOL and preprocess the acquired data accordingly. Then multilayer perceptron (MLP), which is the core of our data-driven approach, is used on the CGD model to determine the appropriate parameter settings of the machine learning model which leads to the combination of best-performing parameters that later on is applied to the analyses of CGCD model. The absolute percentage error of our algorithm is less than 4% for moderate parameter settings and could reach less than 1% when it is optimal. The algorithm also expressed great consistency with its parameters. From this work, it is seen that deep learning supersedes pure numerical simulations of a nanophotonic waveguide, especially in time efficiency. Machine learning has great potential in achieving faster and more accurate waveguide design. |
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T00.00299: ROMNet: Learning Partial Differential Equation Dynamics from Data Using Reduced Order Model Neural Networks A. Ali Heydari Data-driven modeling of dynamical systems is an active area of research. However, current techniques very often require extensive prior knowledge of the governing equations, or are limited to linear or first-order equations. In this work, we propose a neural net-based approach for learning the dynamics of systems described by Partial Differential Equations (PDEs), without requiring any prior knowledge of the system. Specifically, we propose a novel deep learning framework, called Reduced Order Model Network (ROMNet), which consists of three modules responsible for (i) learning a lower dimensional representation of the data, (ii) learning the dynamics and advancing the solution in the reduced latent space, and (iii) mapping the advanced solution from the latent space to the original space. We demonstrate the effectiveness of ROMNet for learning PDE dynamics on complex simulated and real-world data, showing that our model accurately learns unknown linear and nonlinear PDEs (in 2D and 3D). We compare our approach to conventional numerical schemes and find that ROMNet advances the dynamics considerably faster and more efficiently in addition to having comparable accuracy. Our results showcase the implications of deep learning models (such as ROMNet) in learning complex PDEs and the potential to significantly enhance current numerical methods for large systems, as well as to improve the analysis of systems with limited prior knowledge. |
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T00.00300: Extracting Fundamental Parameters of 2-D Natural Thermal Convection Using Machine Learning Mohammad A Boroumand, Gabriele Morra, Peter Mora The Lattice Boltzmann Method (LBM) is an approach for modeling mesoscopic fluid flow and heat transfer, based on modelling distributions of particles moving and colliding on a lattice, which scales to macroscopic flow, as perturbation of the Boltzmann Equation from equilibrium1. We simulate the natural thermal convection of a fluid via LBM in a 2-D rectangular box being heated from below, cooled from above, and use the results as a training dataset to build a deep learning model. A convolutional neural network (CNN) is used to extrapolate the Rayleigh (Ra) and the Prandtl (Pr) numbers used to generate the simulation. The model has a great potential for industrial application like electronic equipment cooling or scientific research such as thermal convection of the Earth’s mantle. |
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T00.00301: An action-oriented, data science-driven approach to make the most of the wind and solar power complementarity Sonia Jerez, David Barriopedro, Alejandro García-López, Raquel Lorente-Plazas, Andrés M Somoza, Judit Carrillo, Ricardo M Trigo Solar and wind power play a main role in the transition toward decarbonized electricity systems, being at the core of climate change mitigation strategies. However, their integration in the energy mix is highly compromised due to the intermittency of their production, at the expense of weather and climate variability. To face the challenge, here we present research about actionable strategies for wind and solar photovoltaic facilities deployment that exploit their complementarity in order to reduce the volatility of their combined production at its minimum. The developed methodology is based on data science techniques and has been implemented in an open-access step-wise model called CLIMAX. It first clusters regions with homogeneous temporal variability of the resources (from long, gridded climate datasets), and then determines the optimal shares of each technology over such regions under a variety of customizable restrictions and conditions. In a simplistic application of the model, aimed at illustrating its performance, we set the goal of narrowing the monthly deviations of the total wind-plus-solar electricity production from a given curve (here, the mean annual cycle of the total production) across five European regions. The results showed that the optimal siting of the power units identified by CLIMAX reduces the standard deviation of the monthly anomalies of the total wind-plus-solar power generation by up to 20% without loss in the mean capacity factor as compared to a base scenario with an evenly spatial distribution of the installations, in both cases considering current shares of each technology. This reduction further improves (up to 60% in specific regions) if the total shares of each technology also participates in the optimization game. Therefore, despite the experimental and pilot nature of this CLIMAX application, these results prove the ability of CLIMAX to provide practical guidance to energy policy decision-makers for the design of the next-generation renewable energy scenarios. |
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T00.00302: Investigating complex collision behavior of inertial active particles using statistical methods and machine vision Farbod Movagharnemati, Nicholas Brubaker, Wylie W Ahmed We explore a macroscopic active matter system with centimeter scale robotic crawlers. In this system, our self-propelled particles are subject to both active noise and inertia. This is distinct from microscopic systems where inertial effects are often ignored or much larger systems where the role of noise is minimal. Our crawlers (i.e. Hexbugs) use an internally rotating motor to drive motion across a dry surface to exhibit Brownian-like motion with inertial persistence. The crawlers are housed within a lightweight circular container to create a hexbug-cup composite particle that is self-propelled and is geometrically isotropic. The resulting collisions between the active particles and their confining environment are surprisingly complex and exhibit rich behavior beyond that expected for elastic or inelastic interactions.. We use particle tracking and image processing techniques to track the motion and infer fluctuating forces of our self- propelled particles on flat and curved surfaces. Using statistical methods and machine learning we investigate collision behavior for this active system. |
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T00.00303: COMPUTATIONAL PHYSICS
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T00.00304: Testing Unification, Dark Matter and Neutrino Masses with Gravitational Wave Detectors Kassandra Garcia, Erika Pierre, Bartosz Fornal Two of the most pressing unanswered questions in particle physics concern the nature of dark matter and the origin of neutrino masses. I will discuss how to explain those mysteries within the framework of a new theory unifying baryon number and color into an SU(4) symmetry, and with lepton number promoted to a U(1) gauge symmetry. The spontaneous breaking of this new symmetry leads to the appearance of neutrino masses. The model enjoys a unique gravitational wave spectrum, including a simultaneous presence of a first order phase transition signal and either a cosmic string or a domain wall signal, all within a similar frequency range. Such signatures can be used to determine the scalar content of the theory at the high scale. I will present how near-future gravitational wave experiments like DECIGO, Big Bang Observer, Einstein Telescope and Cosmic Explorer can be utilized to look for such novel signatures. |
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T00.00305: Probing the Origin of Neutrino Masses via Gravitational Waves from Cosmic Strings Alejandra F Leon, Jessica Bosch, Bartosz Fornal The Standard Model of elementary particles does not explain the origin of neutrino masses nor the domination of matter over antimatter in the Universe. One of the most elegant extensions of the theory providing solutions to those problems involves postulating the existence of heavy right-handed neutrinos and a new U(1) gauge symmetry, leading to the seesaw mechanism for neutrino masses. The breaking of this U(1) symmetry triggers the emission of gravitational waves in the early Universe via cosmic strings, domain walls, and first-order phase transitions, potentially detectable today. Focusing on the special case when the extra U(1) symmetry is either lepton number (L) or baryon minus lepton number (B-L), I will show how to probe different types of seesaw mechanisms (I, II, and III) in upcoming gravitational wave experiments. In particular, I will compare the expected cosmic strings signatures determined using the loop distribution functions from Blanco-Pillado et al. (2014) and Lorenz et al. (2010). If there are two U(1) symmetries at the high scale, one of which is broken via two scalars, a novel and unique gravitational wave signal may arise, involving a simultaneous presence of cosmic string and domain wall signatures. This type of signal has not been considered before, and can be searched for in near-future gravitational wave experiments like LISA, Big Bang Observer, DECIGO, Cosmic Explorer, and Einstein Telescope. |
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T00.00306: Gravitational Wave Signals from Domain Walls as Tests of the Seesaw Mechanism Jessica Bosch, Alejandra F Leon, Bartosz Fornal Neutrinos are the least understood particles of the Standard Model. The mechanism behind their nonzero masses is unknown and requires postulating the existence of new particles and interactions. Given that the measured neutrino masses are very small, the physics behind their generation is naturally set at a high scale (via the seesaw mechanism), very difficult to probe in conventional particle physics experiments. Surprisingly, this is perfectly suited for being tested in gravitational wave experiments via early Universe domain wall and cosmic string production, as well as first order phase transitions. The simplest UV complete realization of the seesaw mechanism is via a U(1) gauge symmetry broken at a high scale. For concreteness, I am going to consider the case when this U(1) symmetry is either lepton number or baryon minus lepton number (B-L), accompanied by an additional U(1) symmetry, e.g., baryon number, also broken at the high scale. If any of the symmetry breaking proceeds via more than one scalar, this may lead to the production of domain walls through an intermediate Z2 discrete symmetry breaking. One therefore expects a new type of signal involving a double-peaked domain wall spectrum, or a domain wall signal overlaying a cosmic string spectrum. This novel type of gravitational wave signature can be searched for in upcoming experiments like Cosmic Explorer, Einstein Telescope, DECIGO, Big Bang Observer and LISA. |
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T00.00307: Dark Matter and Matter-Antimatter Asymmetry of the Universe from Gravitational Waves Erika Pierre, Bartosz Fornal I will present how gravitational wave detectors can be used to probe theories simultaneously explaining dark matter and the matter-antimatter asymmetry of the Universe. In particular, I will focus on an asymmetric dark matter model extending the Standard Model gauge symmetry by a non-Abelian gauge group, under which the leptons form doublets with new fermionic partners. One of those new fermions is a good dark matter candidate. The particle content of the model causes the effective potential to develop a new vacuum, which leads to a strong first order phase transition. This results in the production of gravitational waves via sound waves and bubble collisions. As our calculations show, the signatures of the model can be probed in upcoming gravitational wave experiments, including Cosmic Explorer, DECIGO, Big Bang Observer, and Einstein Telescope. |
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T00.00308: Strain Driven Anomalous Anisotropic Enhancement in the Thermoelectric Performance of Monolayer MoS2 Saumen Chaudhuri, Amrita Bhattacharya, Amal K Das, Gour P Das, Bhupendra N Dev The anisotropic tuning of the transport and thermoelectric properties of monolayer MoS2 with the application of in-plane tensile strains along the armchair (AC) and the zigzag (ZZ) direction have been explored based on first-principles calculations. Tensile strain, in general, is found to have a diminishing effect on the thermopower and power factor of monolayer MoS2, with greater impact on the p-type carriers. However, considering the intrinsic carrier-phonon scattering, we found that the charge carrier mobility (µ) and relaxation time (τ) increases remarkably for strains along the ZZ direction. Concomitantly, strain along the ZZ direction significantly reduces the lattice thermal conductivity (κL) of ML-MoS2. The combined effect of shortened phonon relaxation time and group velocity, and the reduced Debye temperature is found to be the driving force behind the lowering of κL. The large reduction in κL and increase in τ, associated with the strains along the ZZ direction, acts in unison to result in an enhanced efficiency and hence, improved thermoelectric performance throughout the temperature range of 200K to 900K. Nearly 150% enhancement in the thermoelectric efficiency can be achieved with the optimal doping concentration. We, therefore, highlight the significance of in-plane tensile strains, in general and strains along the ZZ direction, in particular, in improving the thermoelectric performance of ML-MoS2. |
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T00.00309: GPU-Accelerated Simulations of Thermal Transport using Machine Learning Force Fields Anders Johansson, Jennifer Coulter, Andrea Cepellotti, Boris Kozinsky Controlling thermal conductivities of materials is important for a wide range of applications, from thermoelectrics for clean energy generation to electronic devices and thermal barrier coatings. The thermal conductivity is commonly estimated using molecular dynamics simulations within the Green-Kubo formulation. This requires a force field that is both 1) an accurate estimate of the interatomic interactions and 2) fast enough to allow simulations with sufficiently large length and time scales. An accurate force field can also be used to accelerate the calculation of force constants for transport simulations via the Boltzmann transport equation. |
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T00.00310: Combined first principles and many-body theory modelling of x-ray absorption spectra of bulk MgO and SrTiO3 Vijaya Begum-Hudde, Christian W Vorwerk, Tobias Lojewski, Andrea Eschenlohr, Katharina Ollefs, Claudia Draxl, Markus E Gruner, Rossitza Pentcheva We present a comprehensive study of the x-ray absorption spectra (XAS) in two paradigmatic oxides − MgO and SrTiO3, from first-principles calculations. The spectra are calculated by including the quasiparticle corrections with G0W0 (MgO) / within the independent particle approximation (SrTiO3), followed by the excitonic effects by solving the Bethe-Salpeter Equation (BSE). Our results show that inclusion of the electron – core hole interaction with BSE is integral to describe the spectra accurately. The simulated XAS spectra for the O and Mg K-edge (MgO) [1], and O K-edge (SrTiO3) [2] are in excellent agreement with experiment w.r.t. the spectral shape and peak positions. The theoretical Ti-L2,3 edge is concurrent with experiment w.r.t. the energetic positions of the four-peak structure stemming from the crystal-field splitting due to the Ti octahedral coordination in SrTiO3. We also analyze the origin of prominent peaks and identify the orbital character of the relevant contributions by projecting the e-h coupling coefficients from the BSE eigenvectors on the band structure. The real-space projection of the wave functions for the lowest energy exciton of the O K-edge shows a strong localization (MgO), whereas a two-dimensional spread in the x-y plane is observed for SrTiO3. |
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T00.00311: Quasiparticle Energies and Dyson orbitals from Stochastic MBPT in an Optimally Localized Basis Annabelle L Canestraight The GW approximation for excited electronic states successfully predicts quasiparticle (QP) energies and states. This comes at large computational expense: in conventional implementations, we are limited to studying systems with 100s of electrons. Stochastic methods have recently succeeded in predicting QP energies for materials with unprecedented sizes (>10,000 electrons). Here, we extend the methodology to predict QP energies and Dyson orbitals in highly inhomogeneous systems. The key strategy is to downfold the many-body Hamiltonian, i.e., reduce a large system into an active subspace (defined by localized QP basis) and an effective environment. By using stochastically sampled vectors to represent the environment subspace, we are able to find QP energies in the active space from a much lower dimensional problem, provided that the dynamical response is entirely included in our solution. This treatment is completely basis-independent. We demonstrate the success of this method by solving for the orbital energies of a small molecule on a large gold substrate and a nanoparticle. |
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T00.00312: Changes in polarization dictate necessary approximations for modeling electronic deexcitation intensity: Application to x-ray emission Subhayan Roychoudhury, Leonardo A Cunha, Martin P Head-Gordon, David Prendergast Accurate simulation of electronic transitions is critical for complementing spectroscopic experiments and for validating theoretical approaches. Using a generalized framework, we contrast the accuracy and validity of orbital-constrained and linear-response approaches that build upon Kohn-Sham density functional theory (DFT) to simulate emission spectra of electronic origin and propose an efficient approximation, named many-body x-ray emission spectroscopy (MBXES) [1], for simulating such processes. We show analytically and with computed examples that for electronic deexcitation leading to an appreciable change in polarization (i.e., density rearrangement), the adiabatic approximation in a response-based formalism is inadequate for the calculation of oscillator strength. Thus, the change in the electrostatic dipole moment of a finite system can be used as a metric for evaluating the applicability of the adiabatic response-based approach and can be particularly valuable in x-ray emission spectroscopy. On the other hand, MBXES, the flexible method introduced here, can compute oscillator strengths accurately at a much lower computational expense on the basis of two DFT-based self-consistent field calculations. Using illustrative examples of emission spectra, the efficacy of the MBXES method is demonstrated by comparison with its parent theory, orbital-optimized DFT, and with experiments. |
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T00.00313: Quasiparticle, exciton, and optical properties in violet and blue phosphorenes Ju Zhou, Tian-Yi Cai, Sheng Ju Strong many-body effects arising from enhanced electron-electron and electron-hole interactions will give rise to novel phenomena in two-dimensional (2D) materials. Accurate computational method like ab initio many-body perturbation theory is necessary to calculate the quasiparticle and optical properties in 2D materials [1]. In this talk, we will discuss our G0W0-BSE calculations on violet (Hittorf's) and blue phosphorenes, two new 2D candidates in the phosphorus allotropes family. We first demonstrate a direct-wide-band-gap semiconductor with anisotropic electron-hole excitation of Hittorf's phosphorene monolayer [2]. In addition, the relatively large thickness makes it possible to modulate the band gap and optical properties substantially via a vertical electric field and this strong quantum-confined Stark effect shows its potential in 2D optoelectronics devices [3]. For blue phosphorene, we reveal the unusual strain dependence of quasiparticle, optical, and exciton properties, where the funnel effect could be realized to overcome its indirect-band-gap nature for the green or blue light-emitting applications [4]. We also show the stronger exciton effect in few-layer blue phosphorene [5]. Compared to other 2D materials [6], it was revealed that the parallel band structure in these indirect band gap semiconductors plays a crucial role. |
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T00.00314: Towards improving generalization of a neural network by interpretation for topological phases of matter Kacper J Cybinski, Marcin Plodzien, Michal Tomza, Maciej A Lewenstein, Alexandre Dauphin, Anna Dawid Machine learning (ML) promises a revolution in science, similarly as it has already revolutionized our everyday lives. In quantum physics, this tool is especially promising in the detection of phases of matter. However, ML models are also known for their black-box construction, which hinders understanding of what they learn from the data and makes their application to novel data risky. Moreover, the central challenge of ML is to ensure its good generalization abilities, i.e., good performance on data outside the training set. Here, we show how the informed use of an interpretability method called class activation mapping (CAM) and its extensions increases the reliability of a neural network (NN) trained to classify quantum phases. In particular, we show that we can ensure better generalization in the complex classification problem by choosing such a model that, in the simplified version of the problem, learns a known characteristics of the phase. We show this on an example of the topological Su–Schrieffer–Heeger (SSH) model with and without the disorder. This work is an example of how the routine use of interpretability methods can improve the performance of ML in scientific problems. |
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T00.00315: Investigation of transition metal complex representations for machine learning structure-property relationships Akash Ram, Eric C Fonseca, Angel M Albavera Mata, Sijin Ren, Richard G Hennig Molecular magnets have potential applications in quantum computing, spintronics, and sensor development. These molecules display spin anisotropy below their characteristic blocking temperature. Contenders for single molecular magnets are monometallic transition metal complexes. Modeling of these complexes demand high computational cost and is difficult due to strong coupling effects. We investigate the performance of crystal graph neural networks (CGNN) for the prediction of properties using a dataset containing nearly 87,000 transition metal complexes. These properties have been calculated using the TPSSh-D3BJ exchange-correlation functional. Here, we see if the CGNN can predict the HOMO/LUMO gap, metal ion charge, and a variety of other computed energies. We then compare the model performance of the CGNN against neural networks trained with structural descriptor representations, such as the smooth overlap of atomic positions (SOAP). A completed model can be used to filter complexes in a high throughput screening. This work provides the first steps in the development of a machine-learning model for the property prediction of transition metal complexes for single molecular magnet applications. |
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T00.00316: Towards Neural Variational Monte Carlo That Scales Linearly with System Size Or Sharir, Garnet K Chan, Anima Anandkumar Quantum many-body problems are some of the most challenging problems in science and are central to demystifying some exotic quantum phenomena, e.g., high-temperature superconductors. The combination of neural networks (NN) for representing quantum states, coupled with the Variational Monte Carlo (VMC) algorithm, has been shown to be a promising method for solving such problems. However, the run-time of this approach scales quadratically with the number of simulated particles, constraining the practically usable NN to — in machine learning terms — minuscule sizes ( |
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T00.00317: From tensor network quantum states to tensorial recurrent neural networks Dian Wu, Riccardo Rossi, Filippo Vicentini, Giuseppe Carleo Tensor networks (TN) have been extensively used to represent the states of quantum many-body physical systems. Matrix product states (MPS) are suitable to capture the ground state of 1D gapped Hamiltonians but not 2D ones, and More powerful TNs cannot be efficiently contracted in general. We show that any MPS can be exactly represented by a recurrent neural network (RNN) with a linear memory update, and generalize it to 2D lattices using a multilinear memory update. It supports perfect sampling and wave function evaluation in polynomial time, and can represent an area law of entanglement entropy. Numerical evidence shows that it can encode the wave function using a bond dimension lower by orders of magnitude when compared to MPS, with an accuracy that can be systematically improved by increasing the bond dimension. |
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T00.00318: Paramaterizing DFT functionals to recover GW energetics Yuting Chen Density functional theory is the most commonly used electronic structure method to predict the structure of various systems, but DFT loses its predictive power in examining strongly correlated systems. The GW approximation of many-body perturbation theory more accurately captures electron correlation, but its much higher computational expense limits its application. We seek to parameterize a DFT functional based on GW data that is able to recover the more accurate GW results at DFT's lower computational cost. The functional is trained for a given material by a global optimization scheme that determines optimum parameters for existing DFT functionals. The resulting functional is a material-specific DFT functional that recovers the energetics and density coming out of GW data. We validate on a series of molecular examples and solids how well this optimization performs for data that were not included in the original training set. Subsequently, we will use these functionals to optimize geometries and get access to quantities that may be too expensive to be evaluated in GW itself. |
Author not Attending |
T00.00319: Nonequilibrium Green Functions in Linear Time Jan-Philip Joost, Niclas Schlünzen, Michael Bonitz The selfconsistent theoretical treatment of correlation and quantum effects in nonequilibrium beyond one-dimensional systems is a particular challenge that has been successfully attacked with nonequilibrium Green functions (NEGF) methods [1]. However, NEGF simulations are hampered by a cubic scaling of the computation time with the number of time steps Nt. Recently, a dramatic acceleration has been achieved within the G1–G2 scheme [2] by transforming the NEGF equations, within the Hartree-Fock Generalized Kadanoff–Baym ansatz (GKBA) [3], to a time-local form for the single-particle and two-particle Green functions. A detailed discussion of the method and its application to a variety of selfenergies including particle-particle and particle-hole T matrix, GW, and the dynamically screened ladder (DSL) was presented recently [4]. Due to its relation to the single-time BBGKY hierarchy, the G1–G2 scheme can benefit from a variety of well-established techniques of two-particle reduced density matrix (2RDM) theory, such as enforcing contraction consistency or a purification of the dynamics, to further improve its accuracy and numerical stability [5]. A drawback of the G1–G2 scheme is the memory cost needed to store the two-particle Green function. This can be significantly relieved by using a recently developed alternative stochastic approach to the G1–G2 scheme [6]. We present first results for the stochastic GW approximation. |
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T00.00320: Simulating the Fermi-Hubbard model with bosonic tensor network states Wenyuan Liu, Garnet K Chan Tensor network states, such as projected entangled pair states (PEPS), are becoming a powerful tool to simulate 2D strongly correlated systems. Although fermionic tensor networks are widely used, an open question in the field is whether we can efficiently simulate fermion systems with bosonic tensor networks, such as bosonic PEPS, using appropriate fermion-to-qubit mappings, which is more similar in spirit to proposed simulations on quantum devices. Critical questions related to the ease of optimizing such bosonic ansatz remain. In this work, we develop a bosonic PEPS algorithm to simulate the Fermi-Hubbard model, which is mapped to a non-local spin system by a Jordan-Wigner transformation. We compare the results obtained using both fermion and bosonic PEPS, discuss their performance and the possibilities for future improvement. |
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T00.00321: Emergence of Wigner oscillations in a model of real time cooling process: a time-dependent density-functional theory approach DANIEL VIEIRA Friedel and Wigner oscillations are well known phenomena occurring in quantum systems. Specifically, in a system composed by N confined particles, the former are characterized by the presence of N/2 peaks in the density distributions, whereas the last by N peaks. Here, we consider N=2 electrons harmonically confined in one-dimensional quantum dots. It is known that the transition from the Friedel to the Wigner oscillations is induced by the increment of interaction between the electrons. The increment of temperature, on the other hand, acts on eliminating the oscillations. In this context, by employing a time-dependent density-functional theory formalism, we obtain the emergence of Wigner oscillations in a model which simulates a real time cooling process. |
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T00.00322: Finding Dynamical Chaos in Stellar Models Ian S Edwards Stellar structure and evolution models are foundational to much of astrophysics by providing a |
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T00.00323: A Machine Learning Study on the Underlying Structural Origin of Glassy Dynamics Eun Cheol Kim, Bong June Sung Finding an underlying structural origin of glassy dynamics is a challenging problem in the field of the glass transition. In this study, we construct a convolutional neural network (CNN) machine learning model that classifies liquids and glasses of two-dimensional (2D) colloidal suspensions only with structural information. We employ the machine learning model to investigate whether any structural origin would exist for the glass transition. 2D colloidal suspensions are an excellent testbed because the hexatic medium-range crystalline order (MRCO) exists for the 2D polydisperse colloids (2DPCs) while the MRCO is not observed for the 2D binary colloids (2DBCs). We find that when the machine learning model is given only snapshots of 2D colloidal suspensions, the machine learning classifies the suspensions into liquids and glasses, successfully. This indicates that one can employ only structural information to understand the states of the suspensions. More interestingly, the machine learning model trained with only 2DBCs that lacks MRCO can also classify the suspensions of 2DPCs with MRCO structures. This shows that the hexatic MRCO would not be the structural origin of 2DPC. |
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T00.00324: Quantifying thermodynamic properties of texts using Jaynes' principle of maximum entropy Fahd Tarek Hatoum, Kristen P Gram, Jiayu Sui, Effrosyni Seitaridou, Alfred C Farris Jaynes’ principle of maximum entropy can be used to study language by quantifying patterns between specific sequences of letters [1,2]. The empirical frequencies of pairwise letter combinations in the words from a given text are the constraints used to maximize entropy by assigning an interaction potential to each pairwise combination. This framework yields a Boltzmann distribution for the energy probabilities of all possible (real and pseudo) words [1,2]. Thus, we can look at properties analogous to those in thermodynamics such as average energy, temperature, and heat capacity for texts in English from varying authors. By calculating the heat capacity as a function of temperature for the word probability distribution of a given text, we find signals occurring at specific temperatures corresponding to changes in word type and composition. We also find that the probability distribution for the energies of words in a specific text has a characteristic temperature. |
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T00.00325: PySAGES: Enhanced Sampling for Ab Initio Dynamics and Machine Learning Potentials Gustavo R Perez Lemus, Pablo Zubieta, Juan J De Pablo, Yezhi Jin PySAGES is a python library for performing enhanced sampling in molecular dynamics simulations. It provides a friendly interface and allows the user to leverage and write complex collective variables and enhanced sampling methods. Here we show how PySAGES can be coupled to Ab Initio integrators using the ASE interface for enhanced sampling in systems where frist principles accuracy is necessary. We also present how PySAGES can be used as a tool for studying the robustness of machine learned force fields. In particular we evaluate a set of different examples of DeePMD, GAP and Graph Neural Network potentials and look at their reliability for preserving the behavior of a system in term of a selected collection of relevant molecular descriptors. |
Author not Attending |
T00.00326: Quantum Monte Carlo method on asymptotic Lefschetz thimbles for quantum spin systems: An application to the Kitaev model in a magnetic field Petr A Mishchenko, Yasuyuki Kato, Yukitoshi Motome Recently developed quantum Monte Carlo (QMC) method on asymptotic Lefschetz thimbles is a numerical algorithm capable of alleviating the sign problem mostly inevitable in the simulations of quantum many-body systems [1]. In this method, the sign problem is alleviated by shifting the integration domain for the auxiliary fields, appearing for example in the conventional determinant QMC method, from real space to an appropriate manifold in complex space. In this talk, we describe a way to extend this method to quantum spin models with generic two-spin interactions. In particular, we utilize the Hubbard-Stratonovich transformation to decouple the exchange interactions and the Popov-Fedotov transformation to map the quantum spins to complex fermions [2]. As a demonstration, we apply the method to the Kitaev model in a magnetic field whose ground state is predicted to deliver a quantum spin liquid [3]. Specifically, we visualize the asymptotic Lefschetz thimbles in complex space, as well as show that in the low-temperature region the sign of the action is recovered considerably and unbiased numerical results are obtained with sufficient precision [4]. |
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T00.00327: PYSAGES: Funnel restraints for Ligand-Receptor enhanced sampling calculations Gustavo R Perez Lemus, Pablo Zubieta, Juan J De Pablo, Cintia A Menendez One of the lessons that the Covid-19 pandemic left to the scientific community is the need of new efficient and precise methods that can be of great help in speeding drug design and discovery. Protein-Ligand (P-L) interactions can be detailed described using molecular dynamics (MD) simulations coupled with enhanced sampling methods. In the past, coupling complex restraint potentials with the enhanced sampling method known as metadynamics lead to Funnel Metadynamics for calculating free energies in protein complexes. Here, we are proposing the use of funnel-like potentials coupled with an extended set of enhanced sampling methods beyond the metadynamics family to have a faster and more efficient sampling of P-L interactions to speed up the computer aided drug design. |
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T00.00328: Explaining Bose “Cylinder Surface” Units Based Upon Integrals Over Particle-Specific ‘Extrastatic’ Axis for Three Core Interactions in Hemispherical (r#,θ#,φ#,z=X0=±½) Arno Vigen A math approach and 3D engineering provides equilibriums for “cylinder surface” units in Bose proof of statistical mechanics.
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T00.00329: Time-dependent ghost-Gutzwiller wave function Daniele Guerci, Massimo Capone, Nicola Lanata We present a time-dependent extension of the ghost Gutzwiller approximation theory (td-g-GA)[1], that enriches the conventional td-GA [2] description of the out of equilibrium quantum dynamics by introducing auxiliary fermionic degrees of freedom [3-6]. We show that our method is able of treating on equal footing both low-energy quasiparticles and high-energy incoherent excitations, which are commonly referred to as Hubbard bands. Furthermore, as opposed to the standard td-GA theory, the td-g-GA allows capturing the dephasing processes that make local observables thermalise in the infinite dimensional quenched Hubbard model, and provides predictions in excellent agreement with numerically exact frameworks but at a much lower computational cost. |
Author not Attending |
T00.00330: Projection-Based quantum embedding for high spin multiplicities Robert L Smith, Nicholas Mayhall Projection-based quantum embedding is a formally exact density functional theory embedding. By implementing an appropriate post-Hartree Fock method, the electron correlation of a chosen embedded subsystem can be recovered from the mean-field approximation in a systematically improvable way. However, partitioning the embedded subspace to include all local entanglement with the embedded subsystem is not trivial, and there have been many proposed partitioning methods involving localized orbitals. Using a singular value decomposition (SVD) to guide the partitioning of the embedded subspace is a robust way to ensure the invariance of the chosen subspace against orbital deformation while capturing the local correlation energy. Additionally, using an SVD to truncate the virtual subspace is a cost conscience way of prioritizing those virtual orbitals that most contribute to the correlation energy in the chosen active space. To date, SVD partitioning of the embedded subspace has been successfully demonstrated for singlet ground-state systems. Here we present an extension of the SVD-informed subsystem projected atomic orbital decomposition partitioning method to systems with higher spin multiplicities. This method is built on restricted open-shell mean-field orbitals that ensure the fidelity of the subsystem spin, a necessary condition of a well-defined embedding method. Furthermore, the same formalism is naturally extended to an SVD-informed concentric localization and subsequent truncation of the virtual space. |
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T00.00331: Characterizing Termination-Dependent TiS2/H2O Interfaces using Deep-Neural-Network-Assisted Molecular Dynamics Marcos Calegari Andrade, Lesheng Li, Roberto Car, Annabella Selloni, Emily A Carter TiS2 electrodes are promising materials for water desalination devices. However, a fundamental understanding of the TiS2 interface with liquid water is still lacking. For instance, it remains unclear how the physicochemical properties of water are affected by different surface terminations of TiS2. This work describes a series of atomic-scale simulations of liquid water in contact with four different terminations of TiS2: Armchair, Zigzag, Zigzag-L and Zigzag-R. The potential energy surface of these systems is described with a first-principles-based deep neural network potential (DP) trained on molecular dynamics (MD) simulations with forces from density functional theory (DFT) using the SCAN+rVV10 exchange-correlation functional. The DP provides good agreement with experimental results available on bulk TiS2. In addition, the DP accurately reproduces the density distribution of interfacial water near TiS2 predicted by ab initio MD. The density distribution profile of interfacial water depends on the TiS2 surface termination exposed to water. Water is found to spontaneously dissociate only on Zigzag-L, the only surface exposing both 4-fold and 1-fold coordinated Ti (Ti4c) and S (S1C) atoms, respectively. The Armchair, Zigzag and Zigzag-R surfaces contain molecular water strongly bound to undercoordinated Ti atoms, but they have a different influence on the depletion region between first- and second-layer water adsorbed on TiS2. The results reported in this work will help further design and improvement of TiS2-based technologies for capacitive deionization. |
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T00.00332: Quantifying electric potential relaxation in the double layer with molecular simulations Dylan Suvlu, Adam P Willard We use isoconfigurational averaging as an enhanced sampling simulation technique to quantify the nonequlibrium response and relaxation dynamics of an aqueous electrolyte in the presence of constant potential electrodes. We compare and contrast the relaxation times of the poisson potential and effective electric potential at atom centers. Furthermore, we use an unsupervised learning technique to quantify the collective water reorientation dynamics in response to the perturbation from the electrodes. |
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T00.00333: Force fields determination for molecular dynamics through Chebyshev polynomials quadrature points RICCARDO DETTORI Atomistic simulations are a powerful tool to complement experiments, and their accuracy and reliability are ultimately determined by the adopted interaction scheme, which will also dictate the computational expense and hence the limit on the attainable simulation size and timescales. Nowadays, atomistic modeling offers a spectrum of possibilities ranging from a full quantum-mechanical description of the system, but limited to a couple hundreds of atoms, to coarse-grained approaches capable of simulating biomolecules of billions of particles. However, the field of extreme conditions still reprents an open challenge because a fully reactive picture is needed to provide an accurate description of the dynamically changing potential energy surface of the system, but the space and time scales involved impose a serious limit for ab initio simulations. A force matched pairwise reactive interatomic model based on Chebyshev polynomials (ChIMES) has recently shown to retain the accuracy of DFT calculations while guaranteeing the reactive nature of the system in a number of cases. Indeed, force matching techniques need a lot of data, possibly at multiple thermodynamics conditions, in order to yield accurate predictions. In this work, we show how using a cluster approach based on the Chebyshev polynomials quadrature points helps in quickly stabilizing the fitting process, potentially avoiding the problem of highly correlated data and overfitting issues. Furthermore, we show a proof of concept application of how the "Chebyshev quadrature points cluster" can be used as a stand-alone force field, dramatically reducing the number of data required for the determination of the interatomic interactions. |
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T00.00334: Screened range-separated hybrid functionals in the density functional tight-binding method: theory and implementation for periodic systems Tammo van der Heide, Balint Aradi, Benjamin Hourahine, Thomas Frauenheim, Thomas A Niehaus Screened range-separated hybrid (SRSH) functionals within generalized Kohn-Sham density functional theory (GKS-DFT) have been shown to restore the correct 1/(rε) asymptotic decay of the screened Coulomb interaction in a dielectric environment (ε). Major achievements of SRSH include an improved description of optical properties and correct prediction of polarization-induced fundamental gap renormalization in molecular crystals [1]. The density functional tight-binding method (DFTB) is an approximate DFT that bridges the gap between first principles methods and empirical schemes. While RSH have already been accessible within DFTB for molecular systems [2], effort has been made to generalize the theoretical foundation to extended systems beyond the Γ-point. For treating the periodic Fock exchange and its integrable singularity in reciprocal space, we resort to techniques successfully employed by DFT. Starting from the first principles Fock operator, we derive suitable expressions for the DFTB method, using standard integral approximations and their efficient implementation in the DFTB+ software package. Convergence behavior is investigated for, among others, one-dimensional acene chains and three-dimensional bulk systems. |
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T00.00335: Nonlocal pseudopotential method for orbital-free density functional theory Qiang Xu Orbital-free density functional theory (OF-DFT) is an electronic structure method that scales linearly with the number of simulated atoms, making it suitable for large-scale material simulations. It is generally considered that OF-DFT strictly requires the use of local pseudopotentials, rather than orbital-dependent nonlocal pseudopotentials, for the calculation of electron-ion interaction energies, as no orbitals are available. This is unfortunate situation since the nonlocal pseudopotentials are known to give much better transferability and calculation accuracy than local ones. We report here the development of a theoretical scheme that allows the direct use of nonlocal pseudopotentials in OF-DFT. In this scheme, a nonlocal pseudopotential energy density functional is derived by the projection of nonlocal pseudopotential onto the non-interacting density matrix (instead of "orbitals") that can be approximated explicitly as a functional of electron density. Our development defies the belief that nonlocal pseudopotentials are not applicable to OF-DFT, leading to the creation for an alternate theoretical framework of OF-DFT that works superior to the traditional approach. |
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T00.00336: Memory efficient Fock-space recursion scheme for many-fermion correlation functions prabhakar . Green’s function is the standard paradigm to study collective |
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T00.00337: The Lyapunov equation and Green’s functions for non-equilibrium stationary states Michael P Zwolak, Gabriela M Wojtowicz, Marek M Rams Extended reservoir approaches provide a versatile framework for simulating many--body, open quantum systems, including quantum transport. These are frequently benchmarked on non-interacting systems (i.e., ones with quadratic Hamiltonians), necessitating the need for robust, scalable computational tools to provide the exact solution in this scenario. We study two such tools here. The first is the use of the Lyapunov equation that was recently provided as the solution to the accumulative reservoir construction (a bridge unifying two distinct extended reservoir approaches). The second is the use of Green's functions to calculate the correlation matrix of the junction system and the extended reservoir modes. We demonstrate that the Keldysh equation for non-interacting Green's functions is related to the formal solution of the Lyapunov equation. Diagonalization of the (retarded) Green's function, thus, not only provides a route to analytic results for the non-interacting correlation matrix, but also provides a new perspective on the Lyapunov equation. We formulate a third approach by integrating out subsystems of modes in the standard way to yield a system of integrals. |
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T00.00338: Relaxation 1D magnetized, collisionless plasma systems Young Dae Yoon, Gunsu Yun One-dimensional magnetized plasma systems are ubiquitous in the Universe. In Cartesian geometry, magnetic field reversals and current sheets are abundant in planetary magnetospheres and solar wind turbulence. In cylindrical geometry, flux tubes and flux ropes are present as solar coronal loops and astrophysical jets. Although these systems are often regarded as equilibrium solutions, in reality they are more likely to start from disequilibrated states. Here we present the relaxation process of such magnetized, collisionless plasma systems, by classifying single-particle orbits and analyzing phase-space particle dynamics. The process is verified by particle-in-cell simulations and comparisons to spacecraft observations. |
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T00.00339: The extension of Yakubovsky equations to six-body bound states Mohammadreza Hadizadeh We present the extension of Yakubovsky equations to the bound state of six identical particles interacting with pair forces leading to five coupled integral equations, where each Yakubovsky component depends on five Jacobi momentum vectors. For the first numerical implementation, we solve the coupled Yakubovsky equations with s-wave separable interactions. We show the details of numerical implementation and present the preliminary results for six-body binding energies. |
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T00.00340: High Pressure Study of Lithium Carbides Anmol Lamichhane, Husam Farraj, Pikee Priya, Muhtar Ahart, Ravhi Kumar, Santanu Chaudhuri, Jordi Cabana-Jimenez, Russell J Hemley High Pressure Study of Lithium Carbides* |
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T00.00341: Frenkel Excitons in Vacancy-Ordered Titanium Halide Perovskites (Cs2TiX6) Seán R Kavanagh, Christopher N Savory, Shanti M Liga, Gerasimos Konstantatos, Aron Walsh, David O Scanlon High-performance, lightweight solar cells with low-cost and non-toxic substituents are a major target in the field of solar photovoltaics.1,2 Perovskite-inspired materials have emerged as promising candidates for this goal, with researchers employing materials design strategies including structural, dimensional and compositional transformations to avoid the use of rare and toxic elemental constituents, while attempting to maintain high optoelectronic performance. These strategies have recently been invoked to propose titanium-based vacancy-ordered halide perovskites (A2TiX6; A = CH3NH3, Cs, Rb, K; X = I, Br, Cl) for photovoltaic operation, following the initial promise of the Cs2SnX6 compounds.3–5 |
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T00.00342: Accurate electronic ground- and excited-state properties of 2D CrI3 and its heterostructures Daniel J Staros, Panchapakesan Ganesh, Brenda M Rubenstein, kevin gasperich, Anouar Benali The recent explosion of research into 2D materials has been largely motivated by promises of new confinement-driven excitonic and polaronic physics of potential use in future microelectronics. In particular, highly-correlated materials like 2D CrI3 and WTe2 are viable candidates for introducing coupled excitonic and magnetic physics into engineered vdW heterostructures. Here, we both outline progress in a new Diffusion Monte Carlo (DMC)-based method for predicting exciton binding energies (EBE’s) in monolayer CrI3, and investigate induced magnetic and electronic effects in a CrI3/1T’-WTe2 bilayer (BL) using Density Functional Theory and Wannier90, benchmarked against DMC calculations. Our prediction of EBE’s utilizes DMC-obtained quasiparticle gaps and features an excited-state single-determinant Slater-Jastrow trial wavefunction built from natural orbitals obtained from a selected configuration interaction (sCI) expansion of localized, mean-field single-particle orbitals. We also quantify induced charge transfer, magnetic, and topological effects in BL CrI3/1T’-WTe2, and conclude with avenues for extending EBE results to the prediction of bilayer EBE’s. |
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T00.00343: First-principles calculations of shift currents for perovskite solar cell materials Koichi Yamashita, Masanori Kaneko Solar cells using methylammonium lead perovskite as light absorbing materials have achieved an astounding 25.5% conversion efficiency improvement, equivalent to silicon solar cells as of 2022. However, there are concerns about the toxic effects of lead in perovskite solar cell materials on human health and the environment, and there is an urgent need to completely replace lead with a more inert metal. In this study, the shift current in lead-free perovskite solar cell materials is estimated by first-principles calculations to evaluate and predict new lead-free perovskite materials. Shift current is a current generated by the real-space movement of electron clouds in materials due to light irradiation. The evaluation and prediction of materials by analyzing their complex photo-response is expected to be applied not only to solar energy conversion but also to photocatalysts, sensors, and other devices. |
Author not Attending |
T00.00344: An approach to MBPT calculations using positive- and negative-energy electrons James J Boyle Negative-energy solutions of the Dirac equation have been difficult to incorporate into calculations involving positive-energy many-electron systems. Chief among these difficulties include what is known as "degeneracy collapse.'" The primary way of avoiding such difficulties has been to exclude negative-energy states from the many-electron Dirac Hamiltonian using positive-energy-only projection operators. This paper outlines a different approach that both incorporates negative-energy solutions and suppresses their contribution in a rigorous way. By requiring that negative-valued probabilities associated with a conserved current vanish for a linear combination of positive- and negative-energy electron state wavefunctions, an electron wavefunction with both positive- and negative-energy contributions is uniquely defined. Significantly, by balancing a negative-valued probability of a positive-energy state against the positive-valued probability of a negative-energy state, the contribution from the negative-energy state can be inherently suppressed—without the use of projection operators. The use of these electron states is illustrated in barrier-scattering problems. Hydrogenic solutions are also constructed and central-field solutions are considered. Unique aspects of these states are discussed. |
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T00.00345: Employing Supervised and Unsupervised Machine Learning Techniques to Detect the Superfluid Phase Transition of a Strongly Interacting Fermi Gas Daniel Eberz, Moritz Breyer, Andreas Kell, Michael Köhl, Martin Link We employ supervised and unsupervised machine learning techniques to detect the onset of superfluidity in time-of-flight (ToF) of strongly correlated fermions in the crossover from the Bose-Einstein condensation of molecules (BEC) to Cooper pairing of fermions (BCS). While a direct observation of Cooper pairs is already not possible due to their breaking upon release from the trap, the remaining imprint of pairing on the momentum distribution is also strongly obscured by temperature, interactions and inhomogeneities of the harmonic trap. To overcome this, we implement a supervised neural network as an advanced image recognition technique to reconstruct the condensate fraction from singular ToF images, which enables the determination of the phase transition over the whole crossover. In an alternative approach, we apply an autoencoder network in an unsupervised learning procedure to the ToF data, which organizes the data by temperature and interaction in a low dimensional latent space without any additional inputs. We are able to identify a feature in the latent space which we interpret as the superfluid phase transition. |
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T00.00346: Quantum simulation of bilayer Hubbard systems and beyond Nick Klemmer Ultracold atoms in optical lattices offer a unique platform for realizing and studying novel quantum phenomena in many-body systems. Of particular interest is the quantum simulation of fundamental models for strongly correlated matter such as the Hubbard model. While the two-dimensional Hubbard model has been extensively studied in experiments over the last few years, more complex systems are largely unexplored. |
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T00.00347: Disentangling Nontrivial Learning Behaviors in Machine-Learned Transition Metal Force Fields from First Principles Cameron J Owen, Steven B Torrisi, Yu Xie, Simon L Batzner, Albert Musaelian, Lixin Sun, Boris Kozinsky The development of accurate and efficient molecular dynamics force fields are a crucial step in an overall materials discovery workflow that complements experiments with computational simulations. In order to facilitate the ongoing development of automated machine-learned force fields using tools like FLARE and NequIP, we have generated a benchmarking dataset of molten single-element bulk structures with a vacancy defect in order to study the interplay between many body behavior and model performance. This dataset contains ab initio molecular dynamics simulations capturing high-temperature crystalline and melted phases. We attempt to explain the difference in model performance across implementation, levels of descriptor fidelity, and individual systems based on differences in elemental properties, and using interpretable machine learning models, reveal the interplay between elemental properties and many-body character revealed by these differences in performance. |
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T00.00348: GENERAL PHYSICS
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T00.00349: Decrease of the dynamical and spatial variability of the Euro-Atlantic eddy-driven jet stream with global warming Robin Noyelle, Davide Faranda, Vivien Guette, Akim Viennet The atmospheric eddy-driven jet stream is one of the main features of the mid-latitude circulation. Although zonal in climatological mean, the jet stream meanders at meteorological time scales. The jet and its variability have been under great scrutiny in the past years for their role in the triggering of extreme events in mid-latitudes regions. Because of the large natural variability of the jet, the impact of climate change remains elusive. Here we study the eddy-driven jet stream over the Euro-Atlantic sector and assess its dynamical properties in ERA5 and ERA20C reanalysis data set using indicators from dynamical system theory. We then use a causal framework to disentangle the impact of global warming from the impact of natural variability of the climate system on the jet. We find that over the period 1900-2010, global warming decreased the spatial and dynamical variability of the jet. This decrease in variability is connected to an increase in jet persistence and speed. We additionally observe a poleward shift and zonalisation of the jet under global warming. |
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T00.00350: Thermodynamics of the local Hadley circulation over Central Africa Landry T Tchambou
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T00.00351: Metric Perturbation Construction in Kerr Spacetime in Horizon Penetrating Coordinates Mohamed Fawzy Abbas Aly
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T00.00352: Modeling slow- and fast-moving interplanetary magnetic clouds Cristian Bahrim, David Matherne, Evgeny Romashets Inter-planetary disturbances travel through the inner heliosphere (a range of heliodistances from 1 to 216 AU) at speeds larger than that of the ambient solar wind in about 3 to 4 days. The spike speed of the disturbance near the solar activity can reach a maximum speed of 1,000 or more km/sec. Out of more than 50 interplanetary magnetic clouds of toroidal shape analyzed in [1] using formulas from [2], we select two events from May 1997 and April 1999, with large AP-daily index: 55.9 and 46.8, respectively. The time of the launch and the arrival time of the cloud are from [1]. Solar activity which can be related to known geo-magnetic storms is discussed. The theoretical dynamics model developed in [3] is adopted in such a way that real parameters in solar wind (density of the particles, temperature, and interplanetary B-field magnitude) are taken into account. We compare slow- and fast-moving magnetic clouds and the time of travel of the cloud’s center of mass. In our dynamics model, the magnetic disturbances are driven by three forces gravitational forces, drag forces and diamagnetic forces. Near the Earth’s orbit, the diamagnetic force and drag force are competing. |
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T00.00353: Using Color Gradients to Study the Inside-Out Formation of Disk Galaxies at 0.8 ≤ z ≤ 1.0 Karmellah R Buttler, Laura DeGroot In this study, we investigated the inside-out galaxy disk formation theory by deriving U - V rest-frame color gradients of a sample of 408 disk galaxies at 0.8 ≤ z ≤ 1.0. Using HST WFC3 images of the GOODS-N region from the CANDELS and UVCANDELS surveys, U - V color maps were created using PSF convolved postage stamps of galaxies in both the F275W and F125W filters, and surrounding objects in the images were masked out for analysis. Color gradients were analyzed through radial profiling using concentric annuli with widths of 0.5 kpc out to a full radius of ∼25 kpc. We find that 98.8% of the 408 galaxies have negative gradients, 45.3% of which had entire color profiles < 0.5 mag indicating that they are likely dominated by young stars, and 53.5% had profiles that had positive centers (> 0.5 mag centrally) and grew negative with radius. Our results suggest at least that an outside-in disk formation is not supported and at most that an inside-out disk formation is possible. Another potential conclusion is that there are fewer old stars in the galactic disk as radius from the center increases. The remaining 1.2% of galaxies had unusually shaped profiles. In the future, a determination of each galaxy's full radius is necessary to separate the galaxy's faint edge from the background. |
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T00.00354: A validation the velocity of Earth in the CMB reference frame using only jitter. John L Haller •Analysis of 1PByte of data from an atomic clock allows us to validate the velocity of Earth in the CMB reference frame, with 26 sigma of evidence, using 2 novel techniques : |
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T00.00355: Ovals in the Spacetime Plane Michael Lynch There has not been a wide range of explicit research towards representations of well-known Euclidean curves in non-Euclidean geometries. Using a simple non-Euclidean geometry from special relativity, the Minkowskian spacetime plane, we can define and find the locus of a curve. The curve under consideration is the oval and was chosen for study since they retrieve the bipolar conics and have seen applicability in Optics. Finding an oval’s different geometric representation was done using elementary definitions that utilize the notion of a general distance and a curve's bipolar representation. One can now describe the new locus and compare properties with its Euclidean counterpart. This work, in future research, can now be used to investigate relativistic dynamics of constrained trajectories on ovals in the spacetime plane and new solutions to optics problems just like the Euclidean representation. Also, pinpointing physical phenomenon that are contained within the oval equations will give one a particular solution to a problem that depends on spacetime distances in a bipolar construction. Finally, this work grants one with the Minkowskian representations of the ellipse and hyperbola which can also be utilized in applications as well. |
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T00.00356: Energy and Possibility Armin Nikkhah Shirazi A standard conception of energy encompasses the capacity to do work, to transfer heat, or to radiate. Here, I propose a fundamental meaning for this conception in terms of the capacity to transform objective possibilities into fact. After situating this concept within fragments of a proposed new paradigm which explicitly recognizes objective possibilities and is therefore called modal, I demonstrate how energy in each of the standard capacities can be understood in accordance with the proposed conception. A key mathematical tool is what I call the bimodal field, a set of numbers constructed out of the real field which permits a direct mathematical representation of the distinction between mere possibilities and facts. |
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T00.00357: Neutrino Decay in JUNO George Parker The decay of the neutrino mass eigenstates are well-constrained using astrophysical neutrinos, with the exception of neutrino mass eigenstate ν3, which has a much less stringent lifetime bound. In this work, we explore the sensitivity of the Jiangmen Underground Neutrino Experiment (JUNO) to ν3-decay. JUNO is a next-generation reactor neutrino liquid-scintillator detector with enhanced flavour sensitivity, exceptional energy resolution and high statistics, which operates on a medium-baseline and could be uniquely tuned to uncover evidence of neutrino decay. We consider the signature of ν3-decay as damping signatures on the neutrino oscillation spectrum in the case of (1) invisible decay, where the daughter states are not observable; and (2) visible decay, where the daughter states are active neutrinos. We comment on how neutrino decay models can be embedded into larger consistent theories. |
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T00.00358: study of activated carbon Fiber from a lignocellulosic material OMAR RODRIGUEZ The research work tries to rationalize the optimization, characterization, and experimental theoretical analysis that focuses mainly on obtaining activated carbon fibers from lignocellulosic fibers in this case the precursor material analyzed and used is cotton fiber which through molecular simulations will analyze its monomer with its structural properties to understand how it is constituted in its entirety, until obtaining reliable results of transformation. The idea is to fully understand the phenomenon of complete transformation, that is, how the precursor material is subjected to different simple chemical processes with different temperatures and as it oxidizes, how its structure is transformed into an activated carbon fiber. |
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T00.00359: A Simple Approach to Determine Diffusion Coefficient of Salt in Various Food Lisa R Wang, Yifei Jin, Songhe Shen, Liangxi "Nick" Chen, William X Li, Songhe Shen 5 different types of foods are studied, and their diffusion coefficients of salt are experimentally determined with a simple and low-cost method. The foods which are studied include potato, sweet potato, pumpkin, taro, and radish. We pre-cut the foods into a spherical shape with known diameters and then brine them into the pre-mixed salt solution. After a certain soaking time, the ball-shaped piece is taken out and cut out a small piece from its center. A compact salt meter (LAQUAtwin-salt-11) made by Horiba was used to determine the salt concentration. The salt concentration at the center of the piece was measured as the diameter or the soaking time is used as variables. We then fit the measured data with the simulation. We are able to determine the following diffusion coefficient data with good matching between the measurement data and the simulation results. Furthermore, the diffusion coefficient of salt in potatoes was also measured at 100°C. The activation energy is thus determined to be around 74meV or 7.13 kJ/mol. |
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T00.00360: Quantum-Information(QI) AUTOMATIC Shannon Information-Theory(IT) BASED UPON New-comb(1881) Algebraic-Inversions(AI) to ONLY BOSONS() VS. Fantasy "Quantum-Computing"(QC) aka #-Theory aka Arithmetic E Carl-Ludwig Siegel, Marvin Antonoff, Herman Chernoff, Gian-Carlo Rota, Frederic Young Aspect-Clauser-Zeilinger[22;Physics Nobel-Prizes] quantum-entanglement/"teleportation" phy -sics Nobel-(Elegren,Olsson,…)-Committee importance typical media-overhyped magic-quantum-ANYthing/EVERYthing "new" era fantasized-upon to support their choice! But QI is both NOT"new" & NOT "news" since Shannon(48) & Newcomb (1881 )/Benford(38)[benfordonline.net]. Within Aristotle-Siegel "Hierarchy-of-Thinking"(HoT)-ONTOLOGY, quantitatIve-functionaAL::{d:0;1,2,3;4,5,6,7,8,9} within (any/all)-Numbers(#) within (any/all)-Data (D) within (any/all))-Info-rmation(I)=(any/all) Neg-Entropy(- S) functionAL: [I=-S](D(#())): : =log[ [+1+1/d] Antonoff/Siegel[AMS Joint-Mtg(02)] AI to ONLY d=1/[10^[ ~~W]–1] : and ITnoisy-channel-capacity(C)/bandwidth(B) in terms of signal(S)/noise(N)-ratio-theorem =lg[+1+ ] AI to ONLY <N/ S>=1/[2^[]–1] , equals Neg-Entropy (-S) =-k AIto ONLY =1/[e^[]–1]! HoT functionAL intermediates :(any/all)-#s & (any/all)-Ds san -dwIched between { }& I=(- S) are AUTOMATICALLY ! "QC" in #-Theory aka arithmetic?; YES, but trivially since any/all-#() are inherently : 1 + 1 = 2! Both: NOT "new"& NOT"news"! |
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T00.00361: AUTOMATIC NON-"Spooky" Action(s) at ANY/NON-Distance(s) in (w,k)-[Dispersion-Relations]-Space DUALS to (r,t)-[Configuration]-Space, Both Quantum & Classical VS. EPR/Bell-Theorem: "Pure"-Maths.Spaces:(r,t) =VS. {DUALS INTEGRAL-TRANSFORMS} VS.= (,k) E Carl-Ludwig Siegel, Marvin Antonoff, Herman Chernoff, Gian-Carlo Rota, Frederic Young AUTOMATIC NON-"Spooky" Action(s) at ANY/NON-Distance(s) in (w,k)-[Dispersion-Relations]-Space DUAL to (r,t)-[Configuration]-Space, Both Quantum & Classical VS. EPR/Bell-Theorem: Pu-re-Maths.:Classical:Franklin/Fourier(1822)-Laplace(1865)-…-Mellin(1881)-Radon (17)-…-Quant-um:Weyl-Wigner(27)-transform[Cohen["Time-Frequency Analysis"(95)]]. Aspect-Clauser-Zeiling-er[22;Physics Nobel-Prizes]. (r,t)-[Configuration]-Space SANS-(GLOBALITY) =INHERENT-[LOCAL-ITY]=VS.{INTEGRAL-TRANSFORM DUALS EXACT-OPPOSITES} VS.= (w,k)-[Dispersion-Relations]-Space SANS-[LOCALITY]=INHERENT-(GLOBALITY), as summarized within Matsubara/Siegel[Stat-phys-13,Haifa(77);Intl.Conf.Lattice-Dynamics,Paris(77 )]-as summarized in Siegel[J.Non-Xline-So-l.40,453(80);Ferroelectrics(81)] "G…P"-ontology within Siegel S.P.D./FUZZY-ICS-ONTOLOGY with-in Aristotle "Square-of-Opposition"(SoO)-ONTOLOGY within Aristotle/Siegel "Hierarchy-of-Thin-king"(HoT)-ONTOLOGY. Example: magnetism models: ground-state-itinerant Longuet-Higgins (r,t)/Hubbard(k,)(53):[Kemeny/Siegel/Cohen:MSU(70);PSS:(72);ibid.(73);JMMM(77-80);Mag.-Lett.(80)] dual of spin-on-lattice ground-state-localized Lenz/IsIng-(11)! |
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T00.00362: Interaction Energy of an Anisotropically Polarizable Atom and a Polarizable Annular Dielectric Niranjan Warnakulasooriya Mahaguruge, Prachi Parashar, K. V Shajesh Investigations involving the interaction energy of an anisotropically polarizable atom and a polarizable annular dielectric has been limited, until now, to the atom being confined on the axis of symmetry. We show that interaction energy admits exact solutions in terms of complete elliptic integrals and our results generalize the interaction energy for the first time when the atom is off the axis of the symmetry. The generalized interaction energy will allow the stability analysis of the atom. |
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T00.00363: Nonlinear response of diffusive systems Ruchira Mishra, Luca V Delacretaz We use the effective field theory of diffusion to study nonlinear response in thermalizing systems. Focusing on the three and four-point functions of the diffusing density (e.g., energy, spin, or charge density), we identify all transport parameters contributing to these observables, find Kubo formulas for each and establish protocols for their measurement in experiments and numerics on non-integrable lattice or continuum systems. We also discuss out-of-time-ordered correlators, and aspects of quantum chaos that are captured by the hydrodynamic effective field theory. |
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