Bulletin of the American Physical Society
APS March Meeting 2023
Las Vegas, Nevada (March 510)
Virtual (March 2022); Time Zone: Pacific Time
Session D42: Twodimensional Magnetic Topological MaterialsFocus

Hide Abstracts 
Sponsoring Units: DMP Chair: CuiZu Chang, The Pennsylvania State University Room: Room 318 
Monday, March 6, 2023 3:00PM  3:36PM 
D42.00001: Quantum spin Hall and quantum anomalous Hall effects in ABstacked MoTe2/WSe2 Invited Speaker: Kin Fai Mak Moiré materials provide a controllable platform to study the combined effects of strong electronic correlations and nontrivial band topology. Recently, robust quantum spin Hall and quantum anomalous Hall effects have been realized in a single material system, ABstacked MoTe2/WSe2, simply by tuning the gate voltages in a fieldeffect device. In this talk, I will discuss the nature of the different topological states and topological phase transitions in ABstacked MoTe2/WSe2 revealed by combining transport, optical and thermodynamic probes. 
Monday, March 6, 2023 3:36PM  4:12PM 
D42.00002: Electrical manipulation and STM visualization of 1D chiral edge states in a moiré quantum anomalous Hall insulator Invited Speaker: Tiancong Zhu The quantum anomalous Hall (QAH) effect reflects an interplay between magnetism and nontrivial topology and is characterized by nonzero Chern number and chiral edgestates that carry dissipationless current along topologically defined interfaces. The discovery of the QAH effect in van der Waals moiré heterostructures provides a new opportunity for studying this exotic 2D state of matter. Here I will discuss our scanning tunneling microscopy and spectroscopy (STM/STS) measurements of twisted monolayerbilayer graphene (tMBLG), a system that has recently been discovered to exhibit the QAH effect as well as gateswitchable orbital magnetism in transport measurements.^{1} I will first discuss local spectroscopy measurements of the correlated insulating states at bandfillings of ν = 2 and ν = 3 electrons per moiré unit cell, where the ν = 3 state shows a total Chern number of C = 2. Under a small magnetic field, we are able to detect switching of the sign of the Chern number for the ν = 3 state induced by electrostatic gating, a result of the competition between bulk and edge orbital magnetization of the QAH state.^{2} Utilization of this gateswitchable Chern number allows us to directly visualize the chiral edgestate of a moiré QAH insulator for the first time through gatedependent dI/dV mapping. We are additionally able to manipulate the spatial location and chirality of QAH edgestates by controlling local carrier concentration with the STM tip. I will discuss the implications of our experimental results for future electronic devices as well as the important role of local moiré strain in determining the correlated and topological properties of tMBLG. 
Monday, March 6, 2023 4:12PM  4:24PM 
D42.00003: Intrinsic magnetic topological phases in a twodimensional MnPSe3 monolayer Ilyoun Na, Marc Vila Tusell, Sinead M Griffin The recent observation of ferromagnetic (FM) topological insulators provides a promising platform for understanding the interplay between the band topology and magnetic order. Despite this, intrinsic magnetism of monolayer topological systems has not yet been experimentally realized so far. Here, we study the electronic properties of FM MnPSe3 monolayer to identify its topological nontrivial features with firstprinciples densityfunctionaltheory (DFT) calculations and a designed tightbinding (TB) model. We demonstrate that magneticorientationdependent different topological states including the quantum anomalous Hall effect (QAHE) and timereversal symmetry broken quantum spin Hall effect (QSHE) can be obtained in MnPSe3 monolayer, manifesting a promising material realization of topological spintronics in twodimensional ferromagnet. 
Monday, March 6, 2023 4:24PM  4:36PM 
D42.00004: Magnetic and Topological Properties of Quasitwodimensional Ferromagnetic Cr_{2}Te_{3} Sohee Kwon, Yuhang Liu, Hang Chi, Gen Yin, Mahesh R Neupane, Roger K Lake Cr_{2}Te_{3} is a ferromagnetic, quasitwodimensional layered material with perpendicular magnetic anisotropy, strong spinorbit coupling, and nontrivial band topology. Applying density functional theory (DFT) and maximally localized Wannier functions (MLWFs), we extract values for the exchange coupling constants and magnetic anisotropy for a model magnetic Hamiltonian and we determine the band topological properties resulting in the anomalous Hall effect (AHE) as a function of strain. We find that Berry curvature switches sign under compressive strain, which results in a sign change in the anomalous Hall conductivity. The underlying mechanism for the straininduced sign change is a large contribution to the Berry curvature resulting from two nearly degenerate, anticrossing Crbands along highsymmetry paths in the Brillouin zone. These theoretical results are in agreement with the recent experimental results demonstrating that the intrinsic Berry phase mechanism is the primary origin of AHE in Cr_{2}Te_{3} [1]. 
Monday, March 6, 2023 4:36PM  4:48PM 
D42.00005: Anomalous Hall effect in Fe_{3}GeTe_{2}: Microscopic mechanism and uniaxial strain effect Mijin Lim, Byeonghyeon Choi, JeGeun Park, HyunWoo Lee Among the several 2D magnetic van der Waals materials, Fe_{3}GeTe_{2} (FGT) has garnered particular interest as a topological ferromagnetic semimetal. The presence of ferromagnetism with topological physics renders this material a platform for interesting phenomena, such as the enormous Berry phase effects. Here we discuss the uniaxial strain effect on the topological properties of FGT and the microscopic mechanism of the anomalous Hall effect (AHE). This study shows the stability of the AHE and the evidence of a nodal line of FGT under uniaxial strains using firstprinciple calculations and model analysis with symmetries. In addition, the topological origin of the intrinsic AHE is demonstrated that the orbital hybridization is responsible for the substantial Berry curvature near Γ point, which is large enough to compare with the previously reported K point contribution. It has important implications for understanding topological ferromagnetic materials and the discovery of magnetic materials exhibiting stronger topological features. Utilizing such topological stability, a quantum device that is resistant to external noise and information loss can be implemented, which is the subject of intensive global research. 
Monday, March 6, 2023 4:48PM  5:00PM 
D42.00006: Tuning ferromagnetism in 2D magnet/topological insulator heterostructures across room temperature by epitaxial growth Wenyi Zhou, Alexander J Bishop, Xiyue S Zhang, Katherine Robinson, Igor Lyalin, Thow Min Jerald Cham, Ziling Li, Shuyu Cheng, Ryan BaileyCrandell, Yunqiu (Kelly) Luo, Daniel C Ralph, David A Muller, Roland K Kawakami 2D van der Waals ferromagnet is Fe_{3}GeTe_{2} (FGT) has a relatively high Curie temperature (T_{C}) with strong perpendicular magnetic anisotropy (PMA). Also, observation of novel phenomena such as spinorbit torque switching and skyrmion spin textures were reported in this material, which makes it an excellent 2D magnetic candidate to be integrated with topological insulators (TIs) for spinorbit torque studies. Here, we study the optimum growth conditions for the FGT/Bi_{2}Te_{3} system using molecular beam epitaxy, through which we observed different magnetic properties for the heterostructures of different growth conditions. With different growth temperature and Fe:Ge atomic ratio, we are able to controllably achieve above room temperature ferromagnetism. Crosssectional scanning transmission electron microscopy (STEM) was used to characterize our highquality epitaxial van der Waals film. Optical magnetic circular dichroism (MCD) enables us to observe and compare the shape of the hysteresis loops of FGT/Bi_{2}Te_{3} samples grown with different growth conditions and determine their Curie temperature. This in turn gives us more insights into the origin of the elevated Curie temperature in FGT/Bi_{2}Te_{3} heterostructure, leading to a more systematic study of synthesis and magnetic properties of this allvdW 2D magnet/TI heterostructure. In addition, we looked into possibilities of integration of other materials belonging to FGT family (Fe_{m}Ge_{n}Te_{2}) with Bi_{2}Te_{3}. 
Monday, March 6, 2023 5:00PM  5:12PM 
D42.00007: Scanning Tunneling Microscopy Study of Epitaxially Grown Fe_{3}GeTe_{2} Layer on the Topological Insulator Bi_{2}Te_{3} Brad M Goff, Alexander J Bishop, Wenyi Zhou, Roland K Kawakami, Jay A Gupta Introducing magnetism to the surface state of topological insulators, such as Bi_{2}Te_{3}, can lead to a variety of interesting phenomena such as magnetoelectric effects, Weyl semimetal phases, and the quantum anomalous Hall effect. We use spinpolarized scanning tunneling microscopy to study a single quintuple layer (QL) of Fe_{3}GeTe_{2} (FGT) that is grown on Bi_{2}Te_{3} via molecular beam epitaxy. FGT is a 2D ferromagnetic van der Waals material with a Curie temperature (Tc) that can exceed room temperature. Large topographic images show that the FGT grows as isolated islands on Bi_{2}Te_{3} and from Bi_{2}Te_{3} steps. Atomic resolution imaging shows atomic lattices of 3.9(9)Å for FGT and 4.4(0)Å for Bi_{2}Te_{3}. The FGT has a Moire pattern with a periodicity of 4.38(6)nm attributed solely to the lattice mismatch showing that the FGT is rotationally aligned to the Bi_{2}Te_{3}. Much of the surface is covered by a single QL of the FGT, with some small double QL regions. There are also regions with partial terminations, where the second quintuple layer is incomplete. The most common partial termination is the FeGe layer, in which the top two atomic layers are missing. This termination has a distinctive electronic structure and a root 3 reconstruction resulting in a 6.8Å lattice constant on top of the Moire pattern associated with the FGT 3.9(9)Å atomic lattice. Preliminary measurements have been done in a magnetic field with an antiferromagnetic Cr tip to probe the magnetic structure and search for magnetic textures. 
Monday, March 6, 2023 5:12PM  5:24PM 
D42.00008: Spin transport in topological insulator nanoribbons sandwiched between twodimensional magnetic materials Nezhat Pournaghavi, Banasree Sadhukhan, Anna Delin Nontrivial band topology along with magnetism leads to some novel quantum phases. When timereversalsymmetry is broken in 3D topological insulators (TIs) by applying high enough magnetic field or proximity effect, different phases such as quantum Hall or quantum anomalous Hall (QAH) emerge and display interesting transport properties for spintronic applications. The Quantum Anomalous Hall (QAH) phase displays sidewall chiral edge states which leads to the QAH effect. In a finite slab, contribution of the surfaces states depends on both the crosssection and thickness of the system. Having a small crosssection and a thin thickness leads to direct coupling of the surfaces, on the other hand, a thicker slab results in a higher contribution of the sidewall states which connect top and bottom surfaces. In this regard, we have considered a heterostructure consisting of a TI, namely Bi_{2}Se_{3} , which is sandwiched between twodimensional magnetic monolayers of CrI_{3} to study its topological and transport properties. Combining DFT and tightbinding calculations along with nonequilibrium Green’s function formalism, we show that a welldefined exchange gap appears in the band structure in which spin polarised edge states flow. We also study the width and finitesize effect on the transmission and topological properties of this magnetised TI nanoribbon. 
Monday, March 6, 2023 5:24PM  5:36PM 
D42.00009: Evolution of magnetic exchange between transitionmetal atoms in TiS_{2} Patrick J Keeney, Paula M Coelho, Jason T Haraldsen In this study, we examine the magnetic and electrical properties of transitionmetal atoms substituted into 2D titanium disulfide (TiS2). Using density functional theory and SCAN functional, we computationally substituted Ti with vanadium, chromium, and manganese and determined the magnetic ground state and Heisenberg exchange as a function of distance. Through our analysis, we find that, as the transitionmetal atom increases in valance electrons and overall spin, the materials move from a standard FM exchange interaction to an RKKYlike magnetic exchange as the materials transition from semiconductors to metals. 
Monday, March 6, 2023 5:36PM  5:48PM 
D42.00010: Topological switch in a near room temperature van der Waals ferromagnet Han Wu, Lei Chen, Paul T Malinowski, Jianwei Huang, Qinwen Deng, Kirsty Scott, Bo Gyu Jang, Jacob Ruff, Ziqin Yue, Elio Vescovo, SungKwan Mo, Jonathan D Denlinger, Donghui Lu, Makoto Hashimoto, Yu He, Pengcheng Dai, Yimo Han, Robert J Birgeneau, JianXin Zhu, Eduardo H Da Silva Neto, Liang Wu, JiunHaw Chu, Qimiao Si, Ming Yi Twodimensional (2D) van der Waals magnets have offered a large playground for exploring exotic correlated phenomena emerging from the interplay between dimensionality, magnetism, and topology. Their versality also allows a stronger tunability under various experimental tuning knobs. We will present the evidence for a switchable topological phase in a metallic near room temperature van der Waals ferromagnet from high resolution angleresolved photoemission spectroscopy measurements supported by a combination of other experimental techniques and theoretical models. We will demonstrate the topological switching to hinge upon a symmetry change that results in a switching of the electronic state between a magnetic Weyl nodal line phase and a geometrical flat bands phase. Our work not only reveals a rich range of quantum phases emergent in 2D van der Waals ferromagnets, but also uncovers the potential of utilizing site occupancy as a novel degree of freedom for tuning symmetry and therefore topology in quantum materials for the realization of exotic emergent phases. 
Follow Us 
Engage
Become an APS Member 
My APS
Renew Membership 
Information for 
About APSThe American Physical Society (APS) is a nonprofit membership organization working to advance the knowledge of physics. 
© 2023 American Physical Society
 All rights reserved  Terms of Use
 Contact Us
Headquarters
1 Physics Ellipse, College Park, MD 207403844
(301) 2093200
Editorial Office
1 Research Road, Ridge, NY 119612701
(631) 5914000
Office of Public Affairs
529 14th St NW, Suite 1050, Washington, D.C. 200452001
(202) 6628700