Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session A46: Undergraduate Research IRecordings Available Undergrad Friendly
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Sponsoring Units: APS/SPS Chair: Brad Conrad, APS Room: McCormick Place W-470A |
Monday, March 14, 2022 8:00AM - 8:12AM |
A46.00001: Measuring the Adiabatic Non-Hermitian Berry Phase in Synthetically Coupled Mechanical Oscillators. Yaashnaa Singhal, Enrico Martello, Tomoki Ozawa, Hannah Price, Shraddha Agrawal, Bryce Gadway The geometrical Berry phase is key to understanding the behaviour of quantum states under cyclic adiabatic evolution. When generalised to non-Hermitian systems with gain and loss, the Berry phase can become complex, and should modify not only the phase but also the amplitude of the quantum state. Here we measure the adiabatic non-Hermitian Berry phase by using a two-site PT-symmetric quantum Hamiltonian, inspired by the Hatano-Nelson model. We realise this non-Hermitian model experimentally by mapping its dynamics to that of a pair of classical oscillators coupled by real-time measurement-based feedback. As we verify experimentally, the adiabatic non-Hermitian Berry phase is a purely geometrical effect that leads to significant amplification and damping of the amplitude also for non-cyclical paths within the parameter space even when all eigenenergies are real. This experiment demonstrates the importance of geometrical effects that are unique to non-Hermitian systems and paves the way towards the further exploration of non-Hermitian and topological physics in classical synthetic metamaterials. |
Monday, March 14, 2022 8:12AM - 8:24AM |
A46.00002: Anomalous Hall effect from Berry curvature in Ga1-xMnxAs1-yPy films Josue Guerra, Logan S Riney, Jiashu Wang, Seul-Ki Bac, Jacek Kossut, Malgorzata Dobrowolska, Jacek K Furdyna, Michael Smith, Yi-Ting Hsu, Badih A Assaf While the carrier-mediated ferromagnetism in GaMnAs has been extensively studied in the past, the origin of anomalous Hall effect (AHE) in magnetic III-V systems remains elusive. It is also expected that the valence bands of III-Mn-V compounds exhibit a strong Berry curvature, possibly resulting from the strain effects that occur in GaMnAsP grown on GaAs and alter the shape of the valence band. In this work, we measure the AHE in a series of Ga1−xMnxAs1−yPy alloys grown by molecular beam epitaxy on GaAs (100) with varying amounts of P (up to 27%) and Mn (1.5%, 2.9% and 4.1%). Specifically, we carried out extensive measurements of transverse and longitudinal resistivity as a function of both magnetic field and temperature. We find that the Hall conductivity can be tuned by varying the phosphorus concentration y and the conductivity in the metallic regime. Theoretical calculations are underway to relate this behavior to specific changes in the band dispersion of GaMnAsP. |
Monday, March 14, 2022 8:24AM - 8:36AM |
A46.00003: Simulation and experimental evidence of dielectrophoresis in manganite thin films Nicole R Burg, Ambika Shakya, Amlan Biswas Manganite thin films of (La1-yPry)1-xCaxMnO3 (LPCMO) which have been grown on NdGaO3 (NGO) substrates exhibit a state where fluid-like ferromagnetic metallic (FMM) regions can coexist with a charge-order insulating background. It has been shown experimentally that these regions can be realigned using electric fields; a process which could be used in practice to effectively manipulate extremely small ferromagnetic regions. One of the main physical principles which can explain this phenomenon is dielectrophoresis, that is when neutral particles in a fluid experience a net-force due to a locally non-uniform electric field. A C++ code was written to simulate the time dependent dynamics of the FMM regions. Electrodes and circular FMM regions are generated on a grid and the relaxation method is used to find the potentials of the configuration statically. Using the fact that force on the regions is proportional to the gradient of the squared electric field, the regions can be repositioned and their movement over time can be observed. Our simulations support the effects we have observed experimentally, which show electric field induced percolation giving rise to the conditions for electron tunnelling through the insulating regions separating neighboring FMM regions. |
Monday, March 14, 2022 8:36AM - 8:48AM |
A46.00004: Room-temperature ferromagnetism in 0D/2D hybrid systems Tyler M Alba, Nalaka A Kapuruge, Kinga Lasek, Florence A Nugera, Valery Ortiz Jimenez, Manh-Huong Phan, Humberto R Gutierrez Two-dimensional (2D) transition metal dichalcogenides (TMDs) have gained popularity over the past years due to their attractive optoelectronic properties. In this work, we propose a system composed of 2D TMD materials, particularly MoSe2; decorated with nanoparticles containing magnetic elements such as oxides of Mn, V and Fe. The 2D TMDs were synthesized by chemical vapor deposition (CVD) and the nanoparticles were deposited in a thermal evaporator under a high vacuum. Raman and PL spectroscopy were used to study their optical properties; while the morphology and thickness of the samples were characterized via SEM and AFM, respectively. Magnetic measurements performed on MoSe2 films, without the nanoparticles, reveal a weak ferromagnetic response. Similarly, weak ferromagnetism is observed for the nanoparticles deposited directly on a SiO2 substrate, without the TMD films. However, when the nanoparticles are deposited on 2D MoSe2, the 0D/2D hybrid system displays enhanced room-temperature ferromagnetism. Temperature-dependent measurements of saturation magnetization and coercivity indicate stronger magnetic coupling at lower temperatures, which could impact the future development of a new generation of spintronic devices. |
Monday, March 14, 2022 8:48AM - 9:00AM |
A46.00005: Spin dynamics simulation of topological CrPt3 and Co2MnGa magnetic nanoparticles Cole Gibson, Fatai Wahaab, Danisbel Herrera, Bushra Sabir, Jacob Gayles Magnetic nanoparticles have the potential for a variety of applications in medicine, energy, and computing. However, the intersection of nanoparticles and topological magnetic materials is relatively unexplored; typical studies of nanoparticles focus on the small-size, superparamagnetic regime, while studies of topological magnetic materials often focus on bulk-like scales. We use spin dynamics simulations to investigate the crossover from superparamagnetic to single domain topological magnetic states in CrPt3 and Co2MnGa nanoparticles. CrPt3 and Co2MnGa display nontrivial topology in their electronic structure, leading to strong spin-orbit states at the nanoparticle surface due to structural inversion asymmetry. Because Fe3O4 nanoparticles are extensively studied, we utilize them to compare the viability of our topological magnetic nanoparticles results. We simulate five nanoparticle shapes with sizes varying from 1 to 60 nm using the LLG equation dependent on external field sweeps at finite temperatures. Parameters for the Heisenberg exchange, surface DMI, and anisotropy were all obtained from first-principle calculations. Our work presents some of the first results for an entirely new regime of magnetic nanoparticles and could seed novel fields of magnetization studies. |
Monday, March 14, 2022 9:00AM - 9:12AM |
A46.00006: Effects of Topological Structures in Ribbons of Magnetic Amorphous Alloys Narayan Pokhrel, Ihor Sydoryk, Catalin Martin The strong magnetoelastic (ME) coupling in magnetic amorphous alloys (MAA) have been exploited for measuring a variety of physical parameters, such as mass, density, viscosity, humidity, or temperature. When a longitudinal magnetic field is applied, a ribbon of MAA also changes its length. If the magnetic field is then oscillated with variable frequency, a strong induced electromagnetic response (emf) can be detected in a pick-up coil when the oscillating frequency matches the mechanical resonance of the ribbon. In this talk, we will demonstrate how MAA ribbons can provide an elegant, yet relatively simple platform for studying the effects associate with topological structures in mechanical systems. We present experimental measurements of the effects of various hole structures on the vibrational modes of MAA ribbons and compare them with COMSOL numerical calculations. |
Monday, March 14, 2022 9:12AM - 9:24AM |
A46.00007: Growth and characterization of a novel 2D Sn-based single crystal material Cory B Stephenson, Rabindra Basnet, Jin Hu The discoveries of various van der Waals compounds with diverse functionalities have offered great opportunity for two-dimensional (2D) materials research. Here, we report the growth and characterization of the single crystals of a new tin phosphide compound. This compound crystalizes in a layered, van der Waals-type crystal lattice structure and exfoliates easily. The electronic transport characterizations reveal metallic transport properties with large, linear magnetoresistance at low temperatures. Our findings provide a new Sn-based metallic compound for 2D material research. |
Monday, March 14, 2022 9:24AM - 9:36AM |
A46.00008: Experimental observation of topological phase transitions in a one-dimensional elastic string model Luke Thatcher Topological insulators are a type of material that allows the existence of unidirectional currents at the quantum scale. These currents, called edge states, are unaffected by material imperfections, which makes topological insulators an active research topic with potential applications in quantum computing. Protected edge states - analogous to the unidirectional current of electronic topological insulators - have recently been demonstrated not only with electrons, but also with photons, sound waves, and mechanical waves. Using a well-known model of topological insulators known as the Su-Schrieffer-Heeger (SSH) model, we constructed a one-dimensional mechanical model of topological insulators that propagates transverse waves in an elastic string. Our device demonstrated a phase transition between the insulator, conductor, and topological insulator phases of the SSH model, with clearly defined edge states in the topological insulator phases. Our findings are supported both by numerical simulations using the finite element method and a mathematical model that we derived from the mechanics of harmonic oscillators. The simplicity of our device facilitates its construction and observation, making it a valuable teaching tool to visually demonstrate topological phase transitions. |
Monday, March 14, 2022 9:36AM - 9:48AM |
A46.00009: Superconducting phase boundaries and gap symmetry of the candidate topological superconductor In0.8Pb0.2Te Jared Z Dans, Matthew P Smylie, Kaya Kobayashi, Takeshi Takahashi, Masaharu Shirata, Ramakanta Chapai, Wai-Kwong Kwok, Ulrich Welp The family of (Sn,In,Pb)Te compounds is expected to contain members which are topological superconductors. Recently, it was observed that the solubility limit of Pb in In1-xPbxTe can be substantially raised via high-pressure synthesis, forming a cubic NaCl-type structure with an enhancement of Tc from ~3 K to ~5 K. We present the superconducting phase diagram of the x = 0.2 member (Tc ~4.7 K), finding lower and upper critical fields of 3.2 mT and 2.12 T, respectively. We report on a full superconducting gap as deduced from penetration depth measurements using the TDO technique at temperatures as low as ~450 mK, eliminating a nodal, odd-parity topological superconducting state as a possibility. |
Monday, March 14, 2022 9:48AM - 10:00AM |
A46.00010: Interplay between Magnetism and Superconductivity of Fe2.5%TaSe2 through Magnetotransport Dhan Bautista, Alex Liebman-Peláez, James G Analytis Intercalation of magnetic ions into highly-correlated electron systems often leads to novel properties emerging from the interactions between magnetism and other order parameters, such as superconductivity. Here, magnetotransport properties of Fe2.5%TaSe2 have been measured as functions of both temperature and field, across a range of pressure. The Fe-doped compound exhibits an overall negative magnetoresistance, in contrast to the positive magnetoresistance of the pure TaSe2 compound. In addition, an anomalous magnetic hysteresis is present in the doped sample at 2 K. Lastly, under pressure the Kondo effect, driven by spin-spin scattering at dopant sites, gives way to superconductivity. |
Monday, March 14, 2022 10:00AM - 10:12AM |
A46.00011: Superfluidity of two-component fermions at the vicinity of orbital Feshbach resonance Andrew M Vincent, Theja De Silva As a test bed for understanding two-band superconductors, we study the superfluidity of two-component ultra-cold fermions in the presence of orbital Feshbach resonance. Based on a mean-field theory, we develop a theoretical approach and derive analytical expressions for both zero and finite temperature superfluid parameters. We present these superfluid parameters as a function of interaction strength between two fermions. These novel analytical results will serve as guiding schemes for current cold-atom experiments. Further, our results will have an impact on understanding two-band superconductors such as MgB2. |
Monday, March 14, 2022 10:12AM - 10:24AM |
A46.00012: Impurity charge compensation in graphene and its effect on charge transport near the Dirac point Nicholas J Pinto, Kelotchi S Figueroa Nieves, Natalya Zimbovskaya, Chengyu Wen, A T Charlie Johnson Charge transport using ferroelectric (FE) gating was investigated in graphene in the temperature range 300K < T < 350K near the Dirac point (DP). Upon increasing the temperature we observed that the conductivity (s) near the DP switched from a positive to a negative temperature gradient. The switch to a negative temperature gradient moved to higher temperatures and weakened upon moving away from the DP. FE polarization induced impurity charge compensation, together with a temperature dependent graphene-impurity charge separation was responsible for the non-monotonicity in s(T). A self-consistent theory for graphene transport with impurity charge scattering, and phonon scattering was used to analyze the results. Non-monotonic charge transport was also observed in the temperature dependence of the residual conductivity (σr). Theoretical analysis of both σ and σr revealed a temperature independent contribution of 1.16e2/h that was probably inherent to pristine graphene. |
Monday, March 14, 2022 10:24AM - 10:36AM |
A46.00013: The state coherence length as a metric of localization in a disordered solid Jeanpun Antarasen, Jorge O Sofo, Brett Green We define and study a new metric of eigenstate localization, the state coherence length Λ, for both continuous and discrete systems of arbitrary dimension. We demonstrate that it directly measures the spatial extent of individual states, and prove that in the configurational average in the localized regime it reproduces the well-known localization length ξ. Applying the state coherence length to a cubic lattice with Anderson disorder, we show that it can be used to find the critical disorder through a simple scaling argument. We use this approach to find the mobility edge, and our results agree with traditional finite-size scaling methods. Apart from its mean value, i.e. the localization length, we also obtain the full probability distribution of the state coherence length as a function of disorder. |
Monday, March 14, 2022 10:36AM - 10:48AM |
A46.00014: First-principles study of LiAlO2 in tetrahedrally and octahedrally coordinates structures Phillip G Popp, Walter R Lambrecht Ultrawide-band gap (UWBG) semiconductors (band gap > 4 eV) have many potential interesting applications, such as in high-power electronics and deep-UV optoelectronic devices. LiAlO2 is a candidate material for UWBG semiconductors. This project is a first-principles electronic structure study of LiAlO2, focusing on band gap/band structure, bulk moduli of common crystal structures, and transition pressures between different structures. Specifically, we compare the tetragonal γ and orthorhombic β structures (both tetrahedrally coordinated) with the R-3m α structure and a disordered rocksalt type δ structure (both octahedrally coordinated). We calculate these properties using the density functional theory (DFT)-based linearized muffin tin orbital (LMTO) and pseudopotential plane wave methods, as well as the more accurate quasiparticle self-consistent GW (QSGW) approach. We find that the tetrahedrally bonded structures have slightly lower energy than the octahedral ones and a transition to the octahedral phase occurs near 2 GPa. |
Monday, March 14, 2022 10:48AM - 11:00AM |
A46.00015: Surface magnetic switching in lower dimensional ferromagnetic films Addison L Hornsey Ferromagnetic (FM) thin films have long been studied for their technological importance and are essential for magnetic storage devices. Recent work has studied the effects of transition metal dichalcogenides on FM films whose interfaces are a subject of great interest due to their outstanding electrical, magnetic, and optical properties. The addition of an optical layer to a FM material may allow us to externally tune the magnetic properties of the films using light. In this work, we aim to understand the reduced dimensionality effect on the magnetic switching and surface properties of Fe thin films. We studied the impact on the surface magnetic properties of Fe films grown on top of WS2, using the magneto optical Kerr effect, magnetic force microscopy and vibrating sample magnetometry. To conduct our experiments, we used 50 nm and 5 nm Fe films grown on Si substrates, and Fe/WS2 films grown on Si and MgO substrates. We found that the reduced dimensionality of the Fe thin film leads to a decrease in the coercive field (Hc). In the Fe/WS2/Si sample, we observe no change in Hc compared to the reference Fe/Si film. In the Fe/WS2/MgO sample, we observe a slight increase in Hccompared to the reference film. The addition of the optical layer (WS2) preserved the magnetic qualities of Fe, showing that it is possible for the two layers to coexist without degrading the FM properties of the film. |
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