Bulletin of the American Physical Society
APS March Meeting 2021
Volume 66, Number 1
Monday–Friday, March 15–19, 2021; Virtual; Time Zone: Central Daylight Time, USA
Session E51: Topological Materials: Magnetic and Quantum EffectsFocus Live
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Sponsoring Units: DMP GMAG Chair: Seongshik Oh, Rutgers University, New Brunswick |
Tuesday, March 16, 2021 8:00AM - 8:36AM Live |
E51.00001: Theoretical prediction and discovery of antiferromagnetic topological insulators Invited Speaker: Mikhail Otrokov Magnetic topological insulators (MTIs) are narrow gap semiconductor materials that combine non-trivial band topology and magnetic order. Unlike their nonmagnetic counterparts, MTIs may have some of the surfaces gapped due to breaking the time-reversal symmetry, which enables exotic phenomena having potential applications in spintronics. Previously, MTIs were only created by means of doping nonmagnetic TIs with 3d transition metal atoms, however such an approach leads to strongly inhomogeneous magnetic and electronic properties of these materials, restricting the observation of important effects to very low temperatures. Finding intrinsic MTI, i.e. a stoichiometric well-ordered compound, could be an ideal solution to these problems. Using ab initio calculations, we predicted the van der Waals layered compound MnBi2Te4 to be the first antiferromagnetic TI (AFMTI) [1]. To date, many experimental groups confirmed the AFMTI state in MnBi2Te4, with the first observation reported in [1]. In the 2D limit, we predicted MnBi2Te4 to show a unique set of thickness- and field-dependent magnetic and topological transitions, which drive it through the intrinsic quantum anomalous Hall state, its zero plateau (axion insulator), and the Chern insulator state, achieved under external magnetic field, but without Landau levels [2]. These predictions have been confirmed in recent experiments [3,4]. The discovery of the first AFMTI MnBi2Te4 opens a new field that focuses on intrinsically magnetic stoichiometric compounds: several MnBi2Te4-derived MTIs were synthesized right away [5], that will be discussed in the talk along with other AFMTI candidates predicted. |
Tuesday, March 16, 2021 8:36AM - 9:12AM Live |
E51.00002: Exploration of topological states in magnetic topological insulator MnBi2Te4 and transition metal dichalcogenide superconductor WS2 Invited Speaker: Wei Li An intrinsic magnetic topological insulator MnBi2Te4 has been discovered recently, in which the quantum anomalous Hall effect has been realized. However, the detection of magnetism as well as topological states on its surface is still controversial. We obtained high-quality MnBi2Te4 film by molecular beam epitaxy and study its electronic structures by scanning tunneling microscopy (STM) and angle resolved photoemission spectroscopy [1, 2]. Based on our results, we propose a novel layered surface structure of MnBi2Te4, which can explain the current controversies in experimental results. In the second part of my talk, I will show our direct STM observation of Majorana bound states in a new transition metal dichalcogenide WS2 [3]. |
Tuesday, March 16, 2021 9:12AM - 9:24AM Live |
E51.00003: Interplay of magnetism, superconductivity, and topology in the rare-earth diantimonides Jörn Bannies, Mohamed Oudah, Douglas A. Bonn, Sarah A Burke, Meigan Aronson Rare-earth diantimonides RESb2 cover a wide range of physics including superconductivity, magnetism and non-trivial topology. Here, we analyze the interplay between these features in different members of this material class. Sizeable single crystals were grown from self-flux. The materials were characterized by magnetization, specific heat, and electrical transport measurements. DFT calculations were used to elucidate their electronic structure, allowing us to investigate the connections between the presence of topologically nontrivial bands near the Fermi level, and the stability of superconducting states. The RE magnetism provides an additional control of superconductivity, emphasizing that the diantimonides are a versatile ground for investigation of electronic correlations in the presence of novel topological phases. |
Tuesday, March 16, 2021 9:24AM - 9:36AM Live |
E51.00004: Defect Genome of 2d Topological Insulators for High Temperature Quantum Anomalous Hall Effect Anh Pham, Panchapakesan Ganesh Currently experimental realization of the quantum anomalous Hall effect (QAHE) is limited at milli-Kelvin temperatures [1]. As a result, it is imperative that new materials be discovered that can host QAHE at higher operational temperatures. Stable defects (intrinsic/extrinsic) can be used to induce new topologies in synthesizable 2D materials [2, 3]. Starting with existing 2d databases [4,5], we designed a workflow to screen defects that are thermodynamically stable and induce non-trivial magnetic and topological properties in stable 2D topological materials. Our results show that cationic or anionic vacancies can potentially induce QAHE with a high Chern number. In addition, in systems where the d-band participates in the band inversion, we find the Chern number and the band gap to be sensitive to treatment of electronic correlations. We apply the linear-response method [6] to obtain the self-consistent Hubbard ‘U’ to predict the topology and gaps. |
Tuesday, March 16, 2021 9:36AM - 9:48AM Live |
E51.00005: Modeling topological edge magnetoplasmons in a quantum anomalous Hall insulator Taige Wang, Alex Cauchon, Julien Alfaro, Monica Allen Microwave impedance microscopy (MIM) has been widely used to probe the local electromagnetic properties of quantum materials in the GHz regime. The traditional way to interpret the MIM signal is to relate the microwave response to the local electrical conductivity and permittivity scalars. In this work, we develop a theoretical framework that models the microwave response of quantum anomalous Hall (QAH) insulators using a full conductivity tensor description. Our numerical simulations reveal topological edge magnetoplasmons (EMP) that propagate along the edge of QAH samples, which can only be captured in our full tensor description. This allows us to distinguish topological edge currents from trivial conduction channels, which can be achieved by performing microwave imaging experiments in the frequency domain. |
Tuesday, March 16, 2021 9:48AM - 10:00AM Live |
E51.00006: Transport Properties of Fe-doped type-II Weyl semimetal WTe2 Rabindra Basnet, Krishna Pandey, Gokul Acharya, Md Rafique Un Nabi, Aaron Wegner, Jin Hu The interplay of topology and magnetism represents a new playground to explore novel quantum phenomenon. Doping of magnetic atoms in topological semimetals could enable new phenomena arising from the coupling between magnetic, electronic, and topological properties, possibly open a new route for further exploration of electronic and spintronic applications. Here, we report the tuning of electronic properties of type-II Weyl semimetal WTe2 by Fe doping. We successfully synthesized Fe-doped WTe2 single crystals and characterized their structure and transport properties. Our study shows the drastic effects of dilute magnetic impurities in the electronic properties of non-magnetic WTe2, which offers a unique route to explore emergent quantum phenomenon introduced by time reversal symmetry breaking in host Weyl semimetal. |
Tuesday, March 16, 2021 10:00AM - 10:12AM Live |
E51.00007: Material and Spin Transport Characterization in Gd-alloyed Bismuth Selenide Protyush Sahu, Thomas Peterson, Yihong Fan, Junyang Chen, Xavier Devaux, Henri Jaffres, Sylvie Migot, Huong Dang, Jean-Marie George, Yuan LU, Jianping Wang Spin Hall systems have garnered a significant amount of attention recently because of their applications in spintronics. Spin logic devices require a higher resistivity for CMOS integration and cascading. One such example is magneto-electric spin-orbit device, which requires a resistivity > 10 mOhm.cm. Furthermore, scaling of the materials require a homogeneity. We developed a homogenous amorphous material, Gd (40%)-alloyed BixSe1-x (60%), which shows a resistivity of 60 mOhm.cm. TEM shows a uniform distribution of Gd throughout the Bismuth Selenide layer. The temperature dependent resistivity shows 3D Mott hopping which persists till room temperature. We performed second harmonic characterization on BSG (6,8,12,16nm)/CFB(5nm) films. The second harmonic signal shows a strong thermal voltage generated from Joule heating of the interface. We performed spin pumping on the BSG(6)/CFB(5) which shows resonance. Spin Hall efficiency and inverse Edelstein length show frequency dependence. This frequency dependence suggests that the spin-to-charge conversion in the material is affected by the presence of magnetic moments in the material. |
Tuesday, March 16, 2021 10:12AM - 10:24AM Live |
E51.00008: Topological Properties of SnSe/EuS and SnTe/CaTe Interfaces Shuyang Yang, Chunzhi Wu, Noa Marom We use density functional theory calculations to study the electronic structure of epitaxial (111) interfaces of the topological crystalline insulators SnSe and SnTe with the magnetic insulator EuS and the non-magnetic insulator CaTe, respectively. We consider both interface slab models with a vacuum region and periodic heterostructures without vacuum. We find that gaps of 21 meV at the Γ point and 9 meV at the M point arise in the topological state at the SnSe/EuS interface, due to the magnetic proximity effect, which breaks the time reversal symmetry. The surface state at Γ is shifted below the Fermi level by 88 meV and the surface state at M is shifted above the Fermi level by 47 meV, owing to band bending at the interface. By comparison, the topological state at the interface of SnTe/CaTe is unperturbed by the presence of non-magnetic CaTe. Reference: Physical Review Materials 4, 034203 (2020). |
Tuesday, March 16, 2021 10:24AM - 10:36AM Live |
E51.00009: Extremely linear magnetoresistance in strained WTe2 Jason Tran, Junxue Li, Ece Aytan, Kirill Shtengel, Alexander A Balandin, Jing Shi, Peng Wei The Td phase of WTe2 has been shown to be a quantum spin Hall (QSH) insulator in the monolayer limit. Outside this limit, Td-WTe2 acts as a topological semimetal due to the closing of its band gap. This makes it challenging to obtain an intrinsic QSH effect and restricts the coherence length of the QSH edge channels. Recently, it was shown that strain can induce an appreciably large band gap in WTe2 beyond single layer thickness [1]. In this talk, we present our studies of strained Td-WTe2 grown by molecular beam epitaxy (MBE). The strain is achieved by choosing a proper seed layer for Td-WTe2 on sapphire. We have previously shown that layered 2D materials grown by MBE can be strained [2]. We characterize the strain along two characteristic orthogonal axes using in-situ reflection high energy electron diffraction. Transport measurements confirm that our few layer strained Td-WTe2 is gapped, and magneto-transport studies demonstrate an unconventional linear magnetoresistance (MR). The origins of the linear MR, such as diffusive transport of QSH edge channels, will be discussed. |
Tuesday, March 16, 2021 10:36AM - 10:48AM Live |
E51.00010: Six-fold degenerate fermions in PdSb2 Ramakanta Chapai, David E Graf, Rongying Jin Pyrite-type cubic PdSb2 possess six-fold degenerate fermions protected by the non-symmorphic symmetry. By measuring the magnetic field (H) dependence of the magnetic torque τ(H) in single crystalline PdSb2, we observe the de Haas-van Alphen (dHvA) oscillations. In analyzing the the dHvA oscillations with H // [111] direction, five frequencies are identified: Fα = 100 T, Fβ = 127 T, Fγ = 175 T, Fη = 338 T, and Fξ = 436 T. By fitting the experimental data using the Lifshitz-Kosevich equation , the effective masses of these bands are obtained with m*α = 0.062m0, m*β = 0.086m0, m*γ = 0.26m0, m*η = 0.34m0, and m*ξ = 0.42(m0 is the free electron mass). Further analysis of the dHvA oscillations reveals that two of the lightest pockets (α and β) at the R point in the Brillouin zone exhibit non-trivial Berry phase (ΦBα = 0.91π and ΦBβ = 0.83π). These are two of the six-fold degenerate bands at the Fermi level. |
Tuesday, March 16, 2021 10:48AM - 11:00AM Live |
E51.00011: Tuning the symmetry and electronic and topological properties of
two-dimensional transition metal dichalcogenides by alloying Wei Luo, David Geohegan, Mina Yoon Using first principles calculations in combination with combined with evolutionary algorithms, we identify stable and metastable configurations of a two-dimensional alloy of WS2xTe2(1-x) with high thermodynamic stability. The alloy system undergoes the phase transition of its crystal symmetry with the changes in its stoichiometry between S and Te. At the same time, the alloy induces a semiconductor-to-metal transition. Furthermore, a metal states induced by the alloy can become a topological insulator. We discuss the origin of the transitions of their symmetry and the electronic and topological properties, as well as the energetics and kinetics of the alloying processes for experimental synthesis. Our work provides a synthesis route for the realization of 2D TMDs with versatile properties. |
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