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 YY09: V: Topological Phenomena I |
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Sponsoring Units: DMP Chair: Soumya Ray, Indian Institute of Technology Patna Room: Virtual Room 9 |
Wednesday, March 22, 2023 10:00AM - 10:12AM |
YY09.00001: Emergent topological states via digital (001) oxide superlattices Zhiwei Liu Oxide heterostructures exhibit many intriguing properties. Here we provide design principles for inducing multiple topological states in (001) (AMO3)1/(AM’O3)1 oxide superlattices. Aided by first-principles calculations and model analysis, we show that a (SrMO3)1/(SrM’O3)1 superlattice (M = Nb, Ta and M’ = Rh, Ir) is a strong topological insulator with Z2 index (1;001). More remarkably, a (SrMoO3)1/(SrIrO3)1 superlattice exhibits multiple coexisting topological insulator (TI) and topological Dirac semi-metal (TDS) states. The TDS state has a pair of type-II Dirac points near the Fermi level and symmetry-protected Dirac node lines. The surface TDS Dirac cone is sandwiched by two surface TI Dirac cones in the energy-momentum space. The non-trivial topological properties arise from the band inversion between d orbitals of two dissimilar transition metal atoms and a particular parity property of (001) superlattice geometry. Our work demonstrates how to induce non-trivial topological states in (001) perovskite oxide heterostructures by rational design. |
Wednesday, March 22, 2023 10:12AM - 10:24AM |
YY09.00002: Transport and Spin Hall Properties of A15 Phase Ta3Sb Thin Films Jidong S Jiang, Qianheng Du, Ulrich Welp, Ramakanta Chapai, Hanu Arava, John Pearson, Anand Bhattacharya The topological band structures of A15 compounds have been predicted to induce large spin Hall conductance[1]. Here, we have synthesized polycrystalline thin films of the A15 phase Ta3Sb by sputter deposition. The crystal structure and phase purity have been confirmed with X-ray diffraction. Rutherford Backscattering Spectrometry shows a Ta/Sb atomic ratio of 4:1, which is consistent with the known Ta-Sb phase diagram [2] and suggests possible site mixing of Ta and Sb. The electrical resistivity of Ta3Sb thin films increases with decreasing temperature above ~300K, and increases very weakly with further decrease in temperature until the superconducting transition at 0.887K. The dominant charge carriers in the normal state are hole type and their density decreases with decreasing temperature. From the harmonic Hall response of a Ta3Sb/permalloy bilayer structure, the spin-orbit torque efficiency and the spin Hall conductivity of thin film Ta3Sb are estimated to be 0.7 and 7325(hbar/2e) (Ω-1cm-1), respectively. [1] E. Derunova, Y. Sun, C. Felser, S.S.P. Parkin, B. Yan, and M.N. Ali, Science Advances 5, eaav8575 (2019). [2] F. Failamani, P. Broz, D. Macciò, S. Puchegger, H. Müller, L. Salamakha, H. Michor, A. Grytsiv, A. Saccone, E. Bauer, G. Giester, and P. Rogl, Intermetallics 65, 94 (2015). |
Wednesday, March 22, 2023 10:24AM - 10:36AM |
YY09.00003: Precursor Inlet for Metal-Organic Molecular Beam Epitaxy of WTe2 Gregory Lapit, Kevin Hauser, Christian E Matt, Jason D Hoffman, Jennifer Hoffman Transition metal dichalcogenides display promising electronic properties such as tunable superconductivity and quantum spin Hall effects when synthesized as monolayer films. Molecular beam epitaxy (MBE) provides a means to synthesize high-purity films by thermally evaporating atomic species. However, some transition metals such as tungsten (W) have high melting points, requiring e-beam rather than thermal evaporation. The low flux stability of e-beam evaporation makes it hard to synthesize large stoichiometric films. To address this challenge, metal-organic precursors have been used in conjunction with MBE to synthesize WS2 [1]. We adapt this process to synthesize WTe2 by introducing the precursor W(CO)6 into the MBE chamber. We developed a precursor inlet system consisting of a precision dosage valve, a nozzle to direct precursor into the substrate, and localized heating to steer precursor condensation and effusion on the way into the deposition chamber. Using mass spectrometry, we observe the precursor decomposing into its fundamental components. |
Wednesday, March 22, 2023 10:36AM - 10:48AM |
YY09.00004: Non-trivial topology and Fermi surface of the kagome superconductor CsV3Sb5 probed by de Haas-van Alphen oscillation Keshav Shrestha, M. Shi, Thinh Nguyen, Duncan Miertschin, K. Fan, Liangzi Deng, David E Graf, X. Chen, Paul C. W. W Chu The Fermi surface of the kagome superconductor CsV3Sb5 was studied using torque magnetometry. Based on electrical resistance and magnetization measurements, this compound displays a charge density wave order at T* = 95 K and superconductivity at Tc = 3.25 K. The torque signal shows clear de Haas-van Alphen (dHvA) oscillation above 20 T with multiple frequencies up to 10 kT. Angular dependence of dHvA oscillation was carried out to investigate the dimensionality of the Fermi surface. Lifshitz-Kosevich analyses for determining the effective mass of charge carriers, as well as Berry phase calculations, will also be discussed. |
Wednesday, March 22, 2023 10:48AM - 11:00AM |
YY09.00005: Magnetic Dirac gap fluctuation in the intrinsic quantum anomalous hall insulator MnBi2Te4 Qile Li, Iolanda Di Bernardo, Johnathon Maniatis, Daniel McEwen, Michael Fuhrer, Mark T Edmonds Intrinsic magnetic topological insulators such as MnBi2Te4 possess magnetic order and non-trivial band topology and are characterized by a magnetic gap opening in the Dirac cone where chiral edge states reside in atomically thin samples with odd layer thickness. This enables observation of the quantum anomalous Hall effect in five-layer MnBi2Te4, but only at temperatures much lower than the magnetic transition temperature. The origin of such suppression remains an outstanding issue and needs to be overcome in order to improve the temperature at which quantum anomalous Hall effect is observed. Here we use scanning tunnelling microscopy and spectroscopy to show that the magnetic Dirac gap in 5 septuple-layer MnBi2Te4 fluctuates spatially, forming regions that are completely gapless representing metallic puddles and fully gapped regions with gap around 70meV. We further demonstrate the hybridization of chiral edge states with these metallic puddles in the bulk, where puddles serve as conductive pathways that cause dissipation, and therefore, suppress quantum anomalous Hall effect. We reveal that a perpendicular magnetic field well below the spin-flop transition is able to restore the magnetic gap in these puddle regions, confirming they originate from magnetic surface disorder. Our study offers key insight into engineering quantum anomalous Hall effect and lossless transport applications at elevated temperature. |
Wednesday, March 22, 2023 11:00AM - 11:12AM |
YY09.00006: Magnetic and transport study of magnetic topological insulators SHANTANU MAJUMDER, Soumya J Ray We have successfully synthesized three magnetic topological insulators for our study: Mn2Bi2Te5, MnBi2Te4, and MnBi4Te7. Till now, thickness-dependent magnetic behavior, Quantum anomalous effect, and Axion insulator state have been observed in MnBi2Te4. We obtained a good fit with the reported result from Rietveld's analysis. The percentage of a secondary phase of MnTe was observed, which was below 4% in all cases. From the scanning electron microscopy (SEM) measurement, we have confirmed the layered nature of the samples. Elemental analysis verified that the molar percentage of Mn: Bi: Te was 1: 2.2: 4.07 for MnBi2Te4, which is very close to the desired result. For, Mn2Bi2Te5 and MnBi4Te7, we got a satisfactory result. From HRTEM and SAED, we deduced the lattice spacing. We micro-mechanically exfoliated the 2D sheets and performed HRTEM. The selected area of electron diffraction gave information regarding all the highly oriented crystals. From the Curie-Weiss fitting of M-T data, we obtained a transition temperature for Mn2Bi2Te5, MnBi2Te4, and MnBi4Te7 at 11K, 24K, and 13 K (out of plane), respectively. Differential conductance vs voltage measurements at different temperatures revealed the increment in the conductivity as we lowered the temperature below the transition temperature, which also agreed well with the resistivity vs temperature measurements. |
Wednesday, March 22, 2023 11:12AM - 11:24AM |
YY09.00007: First principle exploration of magnetism andtopology Anan B Sarkar Recently there has been a surge in exploring the interplay between magnetism and topology. In the last decade an intensive investigation has been carried out as far as nonmagnetic topological systems are concerned, both from theoretical as well as from experimental perspective. As far as discussing the nontrivial properties of topological systems are concerned, the concept of band inversion, hybridization effect will be of utmost importance. While discussing these, we would also like to mention the effects due to change in the lattice parameters, how the overall topological properties will change, the manifestation of the same will then be reflected in the calculated band structures. The reason being, change in lattice parameters will basically hints towards a change in the hopping terms, if we consider things within the perspective of tight binding model, these along with the influence by different correlation parameters, such as 'Hubbard U' will lead to the emergence of various nontrivial properties. Apart from discussing topological properties with pristine structures, we would also like to discuss some of the newly emerging phenomena, while considering hetero-structures. The advantages of using hetero-structures in discussing these new physics, is that it gives us a freedom to manipulate the distance between one-type of systems to other-type of systems, such as for example we can vary the distance between a non-magnetic systems and a magnetic systems, and hence can observe the proximity effect and related features. We can also prepare low-dimensional hetero-structures, i.e slab consist of different type of systems and can in principle manipulate the magnetic correlation in order to get ferromagnetic, antiferromagnetic systems. |
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