Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session G72: Topological MultilayersFocus Recordings Available
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Sponsoring Units: DMP GMAG DCMP Chair: Xuanyuan Jian, University of Florida; Purnima Balakrishnan, National Institute of Standards and Tech Room: Hyatt Regency Hotel -Jackson Park D |
Tuesday, March 15, 2022 11:30AM - 12:06PM |
G72.00001: Proximity-Induced Magnetism and Interface Coupling in Topological Heterostructures Invited Speaker: Alexander Grutter Whether used as a platform for novel quantum transport or ultra-efficient spintronics, heterostructures incorporating topologically nontrivial materials are among the most exciting playgrounds in condensed matter physics. In these systems, interfacial symmetry breaking has played a prominent role in achieving the desired functionalities. Heterostructures interfacing superconductors with a quantum anomalous hall insulator (QAHI) have been reported to exhibit signatures of Majorana fermions, while two-dimensional systems with strong spin-orbit interactions have long been suspected of harboring skyrmions at interfaces with perpendicular magnetic materials. Magnetic proximity effects have been prominently used across topologically trivial/nontrivial material interfaces to open gaps in the surface states of topological insulators or to induce topological transitions. A proper understanding of magnetic proximity effects at topologically nontrivial interfaces hinges critically on our ability to precisely isolate the properties of the interface from the bulk of the system. By decomposing the magnetic and electronic properties on a layer-by-layer and element-resolved basis, new quantum material systems may be robustly understood and designed. In this talk, I will discuss our recent progress in applying polarized neutron reflectometry in concert with X-ray scattering, spectroscopy and electron microscopy to uniquely identify modeling solutions in the complex and challenging parameter space of topological insulator [(Bi,Sb)2Te3, MnBi2Te4], topological crystalline insulator (SnTe), and Dirac semimetal-based heterostructures (Cd3As2). We will examine approaches for accurately identifying magnetic proximity effects and other forms of magnetic interface coupling. We will conclude with a discussion on the future of ultra-sensitive probes of magnetic interfaces, with a particular focus on highly multiplexing neutron instrumentation. |
Tuesday, March 15, 2022 12:06PM - 12:18PM |
G72.00002: Charge transfer and absence of magnetic proximity effect in EuS(111)/Bi2Se3 heterostructures from ab initio calculations Damien Tristant, Ilya Vekhter, Vincent Meunier, William A Shelton Heterostructures made from magnetic and topological insulators (TIs) promise to form excellent platforms for new electronic and spintronic functionalities. The ferromagnet EuS has emerged as a leading candidate for realizing magnetic proximity effect in these systems. However, detailed understanding EuS/TI interfaces is still lacking. |
Tuesday, March 15, 2022 12:18PM - 12:30PM Withdrawn |
G72.00003: Spacer-Layer-Tunable Magnetism and High-Field Topological Hall Effect in Topological Insulator Heterostructures Xiong Yao, Hee Taek Yi, Deepti Jain, Myung-Geun Han, Seongshik Oh Controlling magnetic order in magnetic topological insulators (MTIs) is a key to developing spintronic applications with MTIs and is commonly achieved by changing the magnetic doping concentration, which inevitably affects the spin-orbit coupling strength and the topological properties. Here, we demonstrate tunable magnetic |
Tuesday, March 15, 2022 12:30PM - 12:42PM |
G72.00004: Design of magnetic topological phases in a van der Waals heterostructures Ilyoun Na, Vsevolod M Ivanov, Sinead Griffin The recent observation of antiferromagnetic topological insulators (AFTIs) provides a promising platform for understanding the interplay between the band topology and magnetic order. Despite this, magnetic topological phases in strongly interacting systems remain largely unexplored. Here, we design a tight-binding model of a van der Waals (vdWs) heterostructure composed of two-dimensional magnets with intrinsic AFM ordering separated by spacer layers, which hosts magnetic symmetry-protected topological phases. We propose a solid-state realization of this model by designing a vdW heterostructure comprised of a 2D magnet monolayer and transition-metal dichalcogenide space layer. Using first-principles calculations, we study the influence of inter-layer coupling, strain and correlations on the magnetic and topological features. |
Tuesday, March 15, 2022 12:42PM - 12:54PM |
G72.00005: Imaging magnetism in AB-stacked WSe2/MoTe2 heterostructures Charles L Tschirhart, Evgeny Redekop, Lizhong Li, Tingxin Li, Shengwei Jiang, Kenji Watanabe, Takashi Taniguchi, Martin E Huber, Kin Fai Mak, Jie Shan, Andrea Young AB-stacked MoTe2/WSe2 moiré heterobilayers host magnetic order and a displacement field-tunable quantized anomalous Hall (QAH) effect. NanoSQUID-on-tip magnetometry is capable of imaging magnetic structure through the top gates of dual-gated heterostructures, allowing us to image magnetic order in electronic phases that are stabilized by electric field. I will present scanning nanoSQUID-on-tip magnetometry and transport characterization of this phase. A quantitative characterization of the magnetization of the Chern insulator can be compared to theoretical models of the magnetism and topology. Quantization of the Hall resistance can also be understood in the context of the magnetic structure. The nanoSQUID microscope can extract local displacement- and density-tuned magnetic phase diagrams with ~100 nm resolution, allowing us to probe local variations in the magnetic phase diagram that contribute to disorder in these devices. |
Tuesday, March 15, 2022 12:54PM - 1:06PM |
G72.00006: Molecular beam epitaxy grown Mn-rich (Sb2Te3)x(MnSb2Te4)y magnetic topological insulators with high Curie temperatures Ido Levy, Haiming Deng, Candice Forrester, Xiaxin Ding, Kaushini S Wickramasinghe, Christophe Testelin, Martha R McCartney, David Smith, Lia Krusin-Elbaum, Maria C Tamargo Magnetic topological insulators such as MnBi2Te4 and MnSb2Te3 were predicted to show intrinsic axion insulator behavior and quantum anomalous Hall (QAH) effect. While a single layer of the material, a septuple layer (SL), is ferromagnetic (FM), the SLs couple antiferromagnetically when stacked into the bulk, making it difficult to achieve zero field QAH conductance. Studies have shown that Mn/Sb antisites foster FM behavior. We have previously grown (Sb2Te3)x(MnSb2Te4)y by molecular beam epitaxy. High crystalline quality materials with compositions varying between 0 and 100% SLs were achieved. Samples with more than a few %SL are FM. Hall resistance measurements show that most of the samples exhibit a Curie temperature (TC) of 20-30K. A subset of the samples having 70-80% SLs show a second FM component with TC values as high as 80K. Preliminary magnetization measurements support the presence of the high TC component in those samples. Possible mechanisms will be considered based on the variations in the distribution of SLs in the samples that may lead to regions of higher TC. Variations of the growth conditions that result in more controlled Mn incorporation, and their effect on the resulting magnetic properties will also be presented. (NSF Grant Nos. DMR-2011738 and HRD-2112550) |
Tuesday, March 15, 2022 1:06PM - 1:42PM |
G72.00007: Current-induced switching of ferromagnetic surface states of topological insulators proximitized by 2D ferromagnets Invited Speaker: Masataka Mogi Spin-momentum locked surface states in topological insulators (TIs) are an ideal platform for spin-related novel functionalities, such as quantum anomalous Hall effects and efficient charge-to-spin conversion. Whereas such functionalities are accomplished by making TIs magnetic through impurity doping or proximizing with magnets, these ways would lead to low effeciency of magnetic control or suppression of the anomalous Hall effect, respectively, possibly due to inhomogenious nature of doping or weak/non-uniform coupling between TI and ferromagnets. To realize efficient coupling between the topological surface states and ferromagnetism, it is essential to find proper materials proximitizing the topological surface states. In this work, by employing molecular beam epitaxy, we fabricate heterostructures consisting of (Bi1-xSbx)2Te3 and 2D ferromagnets such as Cr2Ge2Te6 [1], Fe3GeTe2 [2], and (Zn1-yCry)Te [3]. We establish the magnetic proximity coupling at the well-defined hetero-interface supported by van der Waals force between the two layered materials by observing spatial distributions of elements and magnetization with microscopy and neutron reflectometry techniques and a large (quantum) anomalous Hall effect in transport measurements [3,4]. Then we demonstrate current-induced switching of the ferromagnetic topological surface states via spin-orbit torques [2,5]. These results may facilitate an electrical control of dissipationless topological-current circuits. |
Tuesday, March 15, 2022 1:42PM - 1:54PM |
G72.00008: Characterization of Novel Ferromagnetic Topological Insulator - Antiferromagnetic Insulator Thin Film Heterostructures Ryan T Van Haren, Jason Johnstone, David Lederman Magnetic topological insulators (TIs) in proximity with antiferromagnetic (AFM) insulators have the potential of exhibiting new emergent behavior as a result of the exchange interaction at the interface, including interface magnetic exchange effects, strong spin - orbit coupling bulk electronic transport, and novel topological surface state electronic transport. Here we report on the proximity effects of Mn doped Bi2Te3 system, a ferromagnetic TI with a Curie temperature of ~ 16 K, with a series of MF2 (M = transition metal) AFM ionic crystals. This work will demonstrate how these thin film heterostructures can be grown with high crystal quality via molecular beam epitaxy and discuss their magnetic and electronic properties, including possible meergent behaviors that arise from their interface interactions. |
Tuesday, March 15, 2022 1:54PM - 2:06PM |
G72.00009: Critical behavior of magnetic topological insulators Flavio Nogueira We derive an effective field theory model for magnetic topological insulators and predict that a magnetic electronic gap persists on the surface for temperatures above the ordering temperature of the bulk. Our analysis also applies to interfaces of heterostructures consisting of a ferromagnetic and a topological insulator. In order to make quantitative predictions for MnBi2Te4 and for EuS-Bi2Se3 heterostructures, we combine the effective field theory method with density functional theory and Monte Carlo simulations. For MnBi2Te4 we predict an upwards Néel temperature shift at the surface up to 15%, while the EuS-Bi2Se3 interface exhibits a smaller relative shift. The effective theory also predicts induced Dzyaloshinskii-Moriya interactions and a topological magnetoelectric effect, both of which feature a finite temperature and chemical potential dependence. In addition, we derive the scaling relations for the electronic gap and order parameter and study the critical behavior in detail by means of the renormalization group. |
Tuesday, March 15, 2022 2:06PM - 2:18PM |
G72.00010: Topologically-protected magnetic skyrmion for reducing dissipation beyond the limit Mehmet Cengiz Onbasli, Aykut Onel, Arash Mousavi Cheghabouri, Ferhat Katmis, Mustafa Arikan Coupled magnetic moment and Dirac electron assemblies have recently attracted attention on account of usage for high density data storage and quantum computation. A fundamental difficulty is in bringing such bits of information up to room temperature and stabilizing against other interactions. Here, we modeled multi-layer heterostructure combined with ferromagnet and topological insulator thin films where the robust room temperature topological spin texture (zero-field magnetic skyrmion) was simulated and shown to be controlled and protected by interfacial magnetism. The non-collinear alignment of the interfacial robust spin texture is a crucial ingredient for emerging high density memory and logic devices under zero net or discrete topological charge conditions via using skyrmioniums. Further, we numerically demonstrate the motion of concentric skyrmioniums in different material stacks at zero and room temperatures and compare their nucleation and current-driven motion characteristics. We found that the typical current densities for driving the concentric skyrmioniums on topological insulators is around 2-3 orders of magnitude smaller than those in typical Pt/Co bilayer systems. These results highlight the key role of interface band structure and carrier density. |
Tuesday, March 15, 2022 2:18PM - 2:30PM Withdrawn |
G72.00011: High temperature ideal Weyl semimetal phase and quantum anomalous Hall phase in ferromagnetic BaEuNiOsO6 and its (111) (BaEuNiOsO6)/(BaTiO3)10 superlattice Guang-Yu Guo, Hai-Shuang Lu Weyl semimetals (WSMs) have recently stimulated intensive interest because they exhibit fascinating physical properties and also promise exciting technological applications. So far, however, the few confirmed magnetic WSMs generally have a large number of Weyl points either located away from the Fermi level (EF) or shrouded by nontopological Fermi surface pockets. Based on first-principles calculations, we establish double perovskite BaEuNiOsO6 to be a high Curie temperature (Tc) ferromagnetic WSM with magnetization along the [111] direction, just two pairs of Weyl points at EF and Tc = 325 K. The strong ferromagnetism is attribued to the strong ferromagnetic Ni 3d - Eu 4f - Os 5d coupling induced by the substitution of half of Ba atoms with Eu atoms in Ba2NiOsO6. Moreover, the momentum separation of one Weyl point pair is large, thus giving rise to not only a long (001) surface Fermi arc but also large anomalous Hall conductivity. Intriguingly, as a unique physical result of a ferromagnetic WSM, the (111) BaEuNiOsO6 monolayer (ML) superlattice (BaEuNiOsO6)/(BaTiO3)10}, being its (111) quantum-well structure, is found to be a high temperature (Tc = 210 K) Chern insulator with a large band gap of 90 meV. Thus, double perovskite BaEuNiOsO6 will provide a superior material plotform for exploring fundamental physics of Weyl fermions and its (111) ML superlattices will offer a high temperature magnetic topological insulator for studying exotic quantum phenomena. |
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