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 W23: Superlattices, Heterostructures, and Nanocrystals |
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Sponsoring Units: DCMP Chair: Valentin Crépel, Flatiron Institute (CCQ) Room: Room 215 |
Thursday, March 9, 2023 3:00PM - 3:12PM |
W23.00001: Long-range interlayer exchange coupling in [Fe/MgO]N (100) superlattices: the impact of the Fe thickness Anna L Ravensburg, Gunnar K Pálsson, Victor Ukleev, Jochen Stahn, Björgvin Hjörvarsson, Alexei Vorobiev, Vassilios Kapaklis To explain sequential switching in Fe/MgO superlattices, beyond nearest neighbor interactions need to be included, despite the tunneling mediated interlayer exchange coupling (IEC). Fe/MgO superlattices can be described as coupled quantum wells created by the Fe layers, potentially forming collective electronic states responsible for the long-range nature of the IEC. Previous studies have investigated the influence of the MgO thickness and bilayer repetitions N on the coupling and Fe layer switching. These relate to the barrier width and number of quantum wells, respectively. Here, we further examine the effect of the quantum well extension, in terms of the Fe thickness, on the overall magnetic properties of the superlattices. Using a combination of magneto-optical Kerr effect measurements and polarized neutron reflectometry, we investigate the sequential switching of the individual Fe layers. The coupling strength increases linearly for Fe layer thickness between 12 and 23 Å for MgO barriers of 17 Å. The results shed more light on the physics behind the tunneling mediated coupling Fe/MgO superlattices, highlighting how coupled quantum well states in artificial magnetic structures can affect their mesoscopic magnetic properties. |
Thursday, March 9, 2023 3:12PM - 3:24PM |
W23.00002: Hot Electrons and Photothermal Effect in Chiral Plasmonic Nanostructures: Photochemistry and Growth Alexandre O Govorov, Oscar R Avalos-Ovando, Lucas V Besteiro, Eva Yazmin Santiago Santos The generation of energetic (hot) electrons and the photo-heating effect are intrinsic properties of any optically excited plasmonic nanocrystal [1,2]. High-energy hot electrons and phototemperature contribute to kinetic processes observed in plasmonic photodetectors, colloidal nanocrystals, and metastructures [1,2]. This talk will focus on the theory of hot electron generation and also present related applications for plasmonic photochemistry and chiral plasmonic photocatalysis [3,4,5,6]. |
Thursday, March 9, 2023 3:24PM - 3:36PM |
W23.00003: Electrical Resistance in All-metallic Cluster of Ultra-small Silver Nanoparticles Embedded in Gold Tuhin K Maji, SHREYA KUMBHAKAR, Phanindra Sai, Arindam Ghosh Ultra-small nanoparticles of noble metals, in particular silver (Ag) or gold (Au), have been extensively investigated for their optical, magnetic, chemical, and physical properties. However, putting such structures together in an electrically conducting metallic matrix, where the physical size of each individual nanoparticle is crucial, has proven to be difficult. This is because tunnel barriers caused by surface-protecting ligands, oxidation, etc. frequently hinder real metallic conduction through single or clusters of metallic nanoparticles. These difficulties have been resolved in a cross-linked nanohybrid assembly made of extremely small silver nanoparticles (AgNPs) in an all-metallic matrix of Au by removing the chemical residues. The resulting Ag-Au nanohybrid exhibits metallic behavior where the resistance decreases with decreasing temperature, for all radii (rAg ≈ 1 − 3 nm) and concentrations of AgNPs (average center-to-center distance between two AgNPs d ≈ 4 − 6 nm) from room to cryogenic temperatures (≈ 6 K). Surprisingly, we find that the hybrid's electrical resistivity scales directly with the net surface area of the implanted AgNPs, leading to residual resistivity up to 40 µΩ.m, which is more than two orders of magnitude higher than that of crystalline Au. Our study presents a novel strategy for designing nanostructured metals with precisely controllable electrical transport characteristics. |
Thursday, March 9, 2023 3:36PM - 3:48PM |
W23.00004: Hot Carrier Ground States in Coupled Quantum Dots Adityaa Bajpai, Mark Woodall, Allan S Bracker, Michael Scheibner
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Thursday, March 9, 2023 3:48PM - 4:00PM |
W23.00005: Realization of Nonequilibrium Condensates of Polariton using MOCVD-grown GaAs Microcavity Daegwang Choi, Yong-Hoon Cho, Min Park, Chan-Young Sung, Hyoungsoon Choi Since the observation of polariton condensation in GaAs-based microcavity, molecular beam epitaxy has been traditionally used due to its high-quality growth technique. Meanwhile, metalorganic chemical vapor deposition (MOCVD) has barely been focused on studying polariton condensation, although it is a highly scalable growth technique. Here, we realized that polariton condensation using MOCVD-grown GaAs-based microcavity, which has Rabi splitting values of 10.1 meV. Furthermore, we investigated the occupancy of polariton depending on the polariton density, which shows the nonequilibrium condensates behavior. |
Thursday, March 9, 2023 4:00PM - 4:12PM |
W23.00006: Dative Epitaxy of Heterostructures Chang Huai, Mengying Bian, Xuanpu Zhang, Renat Sabirianov, Shengbai Zhang, Hao Zeng Van der Waals 2D heterostructures provide unprecedented opportunities to realize multifunctionality and emergent phenomena. However, most such heterostructures were realized by exfoliation and restacking. This leads to challenges in interface control and puts limitations on scaling up for practical applications. 2D heterostructures have also been realized by chemical and physical vapor deposition techniques. Recently, an unconventional dative epitaxy has been discovered in CVD grown Cr5Te8/WSe2 heterostructures, where Cr5Te8 is a covalent 2D magnet and WSe2 is a vdW semiconductor. Continuing this line of work, we show that a variety of 2D/2D, 3D/2D heterostructures can be epitaxially grown, with combinations of semiconducting, magnetic, and superconducting properties. Our approach opens up an avenue for realizing new heterostructures with high quality interface for exploration of new phenomena and applications. |
Thursday, March 9, 2023 4:12PM - 4:24PM |
W23.00007: Controlling properties of PbTiO3/SrTiO3 superlattices by photo-excited carriers Dansou Carmel, Charles Paillard, Laurent Bellaiche In the last decade, studies of PbTiO3/SrTiO3 superlattices (PTO/STO Sls) showed that they host exotic phenomena such as negative capacitance. These phenomena often accompany real space topological solitons such as flux closure domain polar skyrmions and vortices. Interestingly, recent studies also showed that light is yet another way to induce new properties and even metastable out-of-equilibrium phases in these Sls. One of such phases is the so-called super crystal phase induced by optical excitation. In this work, using a constrained-Density Functional Theory scheme, we report on the impact of the photo-excited carriers on the electrical polarization, internal electrostatic field, and electronic charge density of monodomain PTO/STO Sls. From energetics and electrostatic analysis, we found that the polarization in the direction close to open-circuit conditions (that is the out-of-plane direction) grows under illumination. On the contrary, the polarization in directions close to short-circuit conditions (that are the in-plane directions) is reduced by illumination, as reminiscent of results in bulk ferroelectrics. These photo-induced features therefore result in the rotation of the polarization towards the out-of-plane direction in the superlattices, explaining some recent experimental observations, and yielding a light-induced structural transition. Using standard semiconducting modelling, we further demonstrate that the photo-excited electrons and holes migrate at opposite PTO/STO interfaces to screen bound polarization charges and reduce the electrostatic depolarizing field. This is the main driving force that favors the out-of-plane direction of the polarization under illumination. |
Thursday, March 9, 2023 4:24PM - 4:36PM |
W23.00008: Polar Vortices in Microwave Electronics Florian Bergmann, Bryan Bosworth, Eric Marksz, Aaron Hagerstrom, Sujit Das, Ramamoorthy Ramesh, Nathan D Orloff Under the right lattice periodicity conditions, internal stress in PbTiO3-SrTiO3 superlattices forces the polarization into a vortex structure. This structure is a polar vortex. Polar vortices have remarkable properties such as negative permittivity. More recently, we observed magnetic-like behavior in polar vortex films, and we suspect could be a form of nanoscale structural magnetism. Structural magnetism can occur when a non-magnetic material exhibits magnetic behavior under an alternating electromagnetic field due to structure. While there are experimental demonstrations of structural magnetism in metamaterials, there are no materials with structural magnetism at the nanoscale. Here, we study complex permittivity of superlattice films versus periodicity as a function of frequency to understand the frequency dependent signatures of vortex formation and how they might be indicative of negative permittivity and structural magnetism. Our measurements show the complex permittivity to 325 GHz both parallel and perpendicular to the vortex core and as a function of bias voltage. If true, such remarkable properties could enable new microwave devices including parametric amplifiers and non-reciprocal devices like circulators. |
Thursday, March 9, 2023 4:36PM - 4:48PM |
W23.00009: Designing strong second order magnetoelectric coupling in ABO3/A'BO3 superlattices Saurabh Ghosh, Sokrates T Pantelides The key requirement of multiferroic materials is strong coupling between polarization (P) and magnetization (M). In magnetoelectric (ME) multiferroic materials, M is a function of P and hence electric field (E), M = f(E). The function f(E) can be linear or quadratic (second order). Here we report prediction of strong second-order ME coupling in oxide superlattices using first-principles density-functional-theory calculations. We consider LaFeO3/LnFeO3 (Ln = La, Sm, Gd, Y, Tm) 1/1 superlattices and show that these systems give rise to ME coupling that is an order of magnitude higher than that of the prototype linear ME Cr2O3. The origin of P in LaFeO3/LnFeO3 is hybrid improper ferroelectricity while M is weak, arising from canted Fe spins. Phonon calculations for the Pmc21 symmetry reveal that three IR active structural modes drive such ME couplings, one leads to linear ME coupling and remains in the Pmc21 symmetry, and the other two modes lead to second order ME coupling (Pm and Pc). We found that the origin of second-order ME coupling is the biquadratic relation between M and the tilting of the BO6 octahedra (a-a-c0). Finally, we discuss how the strength of the second-order ME coupling can be enhanced by strain and by tuning the La/Ln cation radius mismatch. |
Thursday, March 9, 2023 4:48PM - 5:00PM |
W23.00010: Resonant Tunneling Current in an Atomically Designed SrRuO3/SrTiO3 Superlattices Hyeonbeom Kim Superlattices which has a Superlattices that have a strong correlation with each layer have been studied a lot in both electrical and optical applications since the first observation of negative differential resistance [NDR] due to its intrigue band structure. Expecially NDR in low-dimensional materials has been attracted for ultra-low power consuption, simple circuit, and multi-logic application. But still, it is hard to apply to the real application due to the breakdown problem hysteresis behavior, and unipolar propertiy. In this, we designed SrRuO3/SrTiO3 oxide superlattice which shows the differrent tunneling current depend on SrTiO3 thickness. The resonant tunneling occured the resonant state of SrRuO3, and NDR was generated in both top and bottom edge states, which showed bipolar operation. And as SrTiO3 thickness increased, two resonant peaks appeared coming from the dielectric dead layer at SrRuO3/SrTiO3 inferfaces with large hysteresis. The systematical analysis of NDR in superlattices can be a key for the future application. |
Thursday, March 9, 2023 5:00PM - 5:12PM |
W23.00011: Engineering spin anisotropy of $J_{
m eff} = 1/2$ square lattices in artificial iridate superlattice Dongliang Gong, Jian Liu Spin anisotropy plays a decisive role in the magnetic phases of quantum materials. The same magnetic order may have the moments point along different crystallographic axes depending on the competition between anisotropy of different symmetries and may undergo a quantum phase transition to switch the spin axis. Tuning the anisotropy could thus induce new emergent states and control their properties. In this work, we engineer the artificial layered structure of the iridate superlattices to control the spin anisotropy of the Jeff = 1/2 square lattices. In particular, we integrate single-layer and bilayer Jeff = 1/2 square lattices in one superlattice structure since they present XY-anisotropy and c-axis anisotropy, respectively. By performing synchrotron x-ray diffraction, resonant x-ray magnetic scattering, magnetization, and resistivity measurements, we found that the new hybrid superlattice stabilizes a new state that is distinct from single-layer and bilayer magnetic anisotropic systems. The entire hybrid superlattice orders simultaneously through a single antiferromagnetic transition at temperatures similar to the bilayer system but with all the Jeff = 1/2 moments mainly pointing in the ab-plane similar to the single-layer system. The results show that bringing different magnetic anisotropic systems with orthogonal properties in proximity to each other is a powerful way to stabilize a unique state in the system. |
Thursday, March 9, 2023 5:12PM - 5:24PM |
W23.00012: The ab initio prediction of charge transfers, ARPES signatures, and superconducting critical temperatures in misfit heterostructures Drake Niedzielski, Brendan D Faeth, Berit H Goodge, Mekhola Sinha, Tyrel M McQueen, Lena F Kourkoutis, Tomas A Arias We present the first ab initio results for charge transfers, ARPES signatures, and superconducting critical temperatures for misfit materials without an underlying periodic cell. Using refinements of our recently developed Sandwich Mismatched INterface Theory (MINT-Sandwich) method, we explore the aforementioned quantities in the misfit compounds (LaSe)1.14 (NbSe2)1,2. Our results show how to resolve the apparent discrepancy between measured and predicted charge transfer in these misfit compounds, and reveal the true nature charge transfer in these materials. |
Thursday, March 9, 2023 5:24PM - 5:36PM |
W23.00013: Enlargement of band gaps on thermal wave crystals by using heterostructures Jesus Manzanares Martinez Thermal wave crystals are periodic structures that support temperature wave oscillations. In these lattices, band gaps exist for heat flow due to interference phenomena. In this work, we demonstrate how heterostructures—a stack of two different lattices—can be used to increase band gaps. We investigate two distinct periodic structures. The first is a biological composite made up of stratum-like and dermal-like materials where we have found a band gap enlargement from 1.93 to 10.08 Hz. The second is composed of two semiconductors, silicon (Si) and germanium (Ge), where we have designed a heterostructure with a band gap ranging 0.096 to 0.17 Thz. The design of heterostructures to increase band gaps is especially useful when there is a low contrast of material parameters, as is the case of semiconductors. |
Thursday, March 9, 2023 5:36PM - 5:48PM |
W23.00014: Bound states in the continuum in a two-channel Fano-Anderson model Pedro Orellana In this work, we study the formation of the bound states in the continuum (BICs) in a two-channel Fano-Anderson model. We employ the Green's function formalism, together with the equation of motion method, to analyze the relevant observables, such as the transmission coefficient and the density of states. Most importantly, our results show that the system hosts true BICs for the case of a symmetric configuration with degenerate impurity levels, and a complete transmission channel is then suppressed. Finally, we argue that the proposed mechanism could be relevant for the realization of bound states in the continuum in electronic and photonic systems. |
Thursday, March 9, 2023 5:48PM - 6:00PM |
W23.00015: An Experimental Measurement of the Dynamical Casimir Effect in an Optical Cavity Adam Cummings Measurement of quantum vacuum fluctuations as predicted possible by Casimir in 1948 has very little experimental evidence. The first demonstration of the Dynamical Casimir Effect (DCE) was in 2011 using a superconducting quantum interference device. The effect has not been demonstrated in an optical cavity with a varying semiconductor mirror via laser pumping. Theory predicts that in a pumped optical cavity, DCE photon number increases exponentially in time. This may provide a unique opportunity for producing a high number of correlated photons with distinguishable spectra from the quantum vacuum. We can take advantage of the picosecond crystal phase transition time-scale of vanadium oxides acting as a mirror in the optical cavity with rapidly changing boundary conditions such that DCE photons are excited out of the vacuum. HBT interferometry and cryostat pump-probe spectroscopy can fully characterize DCE photons. |
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