Bulletin of the American Physical Society
APS March Meeting 2019
Volume 64, Number 2
Monday–Friday, March 4–8, 2019; Boston, Massachusetts
Session S02: Topological Materials  Magnetic Materials 
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Sponsoring Units: DMP GMAG Chair: Tyrel McQueen, Johns Hopkins Univ Room: BCEC 107A 
Thursday, March 7, 2019 11:15AM  11:27AM 
S02.00001: Theoretical study of topological materials for spintronics Wei Jiang, Tony Low Enabling highly efficient currentinduced magnetization switching is critical to future spintronic applications, and many proposals relies on topological effects for the conversion of charge current to spin current. Recently, the intrinsic spinHall effect (SHE) in the topological materials has been intensely studied and was proposed to play a more important role in the field, because of their extremely large spin Berry curvature. Here, we carried out theoretical studies of different topological materials ranging from topological insulator, Dirac/Weyl semimetal, to topological superconductor, and calculated their intrinsic spinHall conductivity (SHC). The figure of merit for chargetospin conversion is defined as the SHC over the density of state, based on which we propose a family of topological materials for the spintronics devices. 
Thursday, March 7, 2019 11:27AM  11:39AM 
S02.00002: Structural and Physical Properties of Magnetic EuMnSb_{2 }Single Crystals Silu Huang, Xin Gui, Weiwei Xie, Rongying Jin Layered EuMnPn_{2} (Pn = Sb, Bi) has generated immense interest because of the interplay between complex magnetism (Eu and Mn forming two magnetic sublattices) and topological properties. We have successfully grown EuMnSb_{2} single crystals, which form the tetragonal structure (space group P4/nmm) containing Sb square net. Both inplane (ρ_{ab}) and caxis (ρ_{c}) resistivities show semiconductorlike behavior with an anomaly at T_{N} ~ 20 K. Magnetization measurements indicate that there is an antiferromagnetic (AFM) transition at T_{N}. Upon the application of the magnetic field along the c axis, the inplane magnetoresistance (MR_{ab}) changes sign from positive at T > T_{N} to negative at T < T_{N}, while MR_{c} reveals the opposite trend. This indicates that magnetic interactions are different between the ab plane and c direction. Further discussion will be presented. 
Thursday, March 7, 2019 11:39AM  11:51AM 
S02.00003: Crossover of Quantum Anomalous Hall to Topological Hall Effects in Magnetic Topological Insulator Sandwich Heterostructures Jue Jiang, Di Xiao, Fei Wang, Jaeho Shin, Jianxiao Zhang, Domenico Andreoli, Run Xiao, Yifan Zhao, Morteza Kayyalha, Ling Zhang, Jiadong Zang, ChaoXing Liu, Nitin Samarth, CuiZu Chang, Moses H. W. Chan Electronic band structures with nontrivial topology in momentum space and magnetic spin textures in real space have attracted enormous attention in the past decade since they harbor elegant physics relevant to the Berry curvature. The quantum anomalous Hall (QAH) effect, which is induced by the Berry curvature in the momentum space, supports dissipationfree chiral edge states. The topological Hall (TH) effect is a transport signature of the chiral spin textures that are a consequence of Berry curvature but in realspace. Both QAH and TH effects have been separately reported in magnetically doped TI materials and thus it is natural to ask if both phenomena can coexist in a single sample. Here, by inserting a TI layer between two magnetic TI layers to form a sandwich heterostructure, we observed the crossover from the QAH to TH effects through tuning electrostatic gate voltage. Our theoretical modeling suggests that the inserted TI layer decouples the two magnetic TI layers. As a consequence, the strong DzyaloshinskiiMoriya interaction in each magnetic TI layer can give rise to chiral spin textures and lead to the TH effect. Our study provides us a new understanding of the interplay between the momentumspace and realspace Berry curvatures in magnetotransport phenomena. 
Thursday, March 7, 2019 11:51AM  12:03PM 
S02.00004: Quantum anomalous Hall effect at the interface between magnetic and topological crystalline insulators Jinwoong Kim, David Vanderbilt By employing tightbinding and firstprinciples calculations, we investigate the possible appearance of the quantum anomalous Hall (QAH) effect at the interface between topological crystalline insulators (SnTe, SnSe) and magnetic insulators (EuO, EuS, EuSe). For a surface Dirac cone associated with a band inversion in the bulk, a mass gap acquisition via an effective Zeeman field is a subject of broad interest because of the potential for exotic thinfilm states such as the QAH and axionic phases. A number of studies have demonstrated the appearance of such states by using diverse interfacial and magneticelementdoped systems in agreement with predictions. Although achieving a large mass gap is critical for further investigations and room temperature devices, the microscopic mechanisms determining the size of the mass gap have not been clearly addressed. In this study, we enumerate several combinations of topological crystalline insulators and magnetic insulators in a search for an optimal electronic structure, where a large mass gap is isolated inside a bulk insulating gap. The underlying mechanisms and their dependence on factors such as magnetization orientation will be discussed. 
Thursday, March 7, 2019 12:03PM  12:15PM 
S02.00005: Local magnetism in a correlated Kagome magnet with massive Dirac Fermions Yangmu Li, Qi Wang, Ryan Desautels, Qianheng Du, Weijun Ren, Zhidong Zhang, Cedomir Petrovic, Lisa DeBeerSchmitt, Igor Zaliznyak, Weiguo Yin, Hechang Lei, John Tranquada Recent photoemission and scanning tunneling experiments revealed that Fe_{3}Sn_{2}, a stronglycorrelated Kagome magnet, features massive Dirac fermions and an intrinsic electronic nematicity [1, 2]. DFT calculations show that the Dirac mass depends significantly on the local magnetic moment. The electronic nematicity also relates to local magnetism through the spinorbital coupling. Here, we present our smallangle neutron scattering and angleresolved charge transport results in combination with DFT calculations to characterize the complex role of local magnetism in Fe_{3}Sn_{2}. 
Thursday, March 7, 2019 12:15PM  12:27PM 
S02.00006: Anomalous Hall Effect in Intrinsic Antiferromagnetic Topological Insulator MnBi_{2}Te_{4} Seng Huat Lee, Yanglin Zhu, Yu Wang, Zhiqiang Mao MnBi_{2}Te_{4} has recently been predicted to be an intrinsic antiferromagnetic topological insulator (AFMTI)^{1}. This material is also predicted to show ferromagnetism if its dimensionality is reduced to 2D and support other topological states, including typeII magnetic Weyl semimetal state under magnetic fields and Majorana fermions at the interface with a superconductor. Its surface states and magnetic phase transition have been experimentally observed in both bulk^{2} and thinfilm samples^{3}. The material provides an excellent platform to study various exotic physics as well as the realization of the quantum anomalous Hall effect at higher temperatures. Here, we report the synthesis of highquality bulk single crystals of MnBi_{2}Te_{4} by meltgrowth technique. Magnetictransport measurements on bulk samples demonstrated the first observation of the anomalous Hall effect. 
Thursday, March 7, 2019 12:27PM  12:39PM 
S02.00007: Antiferromagnetic topological insulator MnBi_{2}Te_{4} Mikhail Otrokov, Igor P Rusinov, Maria BlancoRey, Martin Hoffmann, Alexandra Yu Vyazovskaya, Sergey V Eremeev, Yury M Koroteev, Arthur Ernst, Pedro M Echenique, Andres Arnau, Evgueni Chulkov Using ab initio and Monte Carlo calculations we predict the van der Waals layered compound MnBi_{2}Te_{4} to be antiferromagnetic (AFM) topological insulator [1], which is further confirmed experimentally [1]. MnBi_{2}Te_{4 }appears to be invariant with respect to the combination of the timereversal and primitivelattice translation symmetries, giving rise to the Z_{2 }topological classification of AFM insulators, and Z_{2}=1 for MnBi_{2}Te_{4}. Its (0001) surface, breaking the combined symmetry, shows a giant gap in the topological surface state thus representing a promising platform for the quantized magnetoelectric effect observation. In the 2D limit, MnBi_{2}Te_{4} shows a unique set of thicknessdependent magnetic and topological transitions, which drive it through FM and (un)compensated AFM phases, as well as quantum anomalous Hall (QAH) and intrinsic zero plateau QAH states [2]. 
Thursday, March 7, 2019 12:39PM  12:51PM 
S02.00008: Large anomalous Hall effect in topological insulators with a proximitized ferromagnetic insulator Masataka Mogi, Taro Nakajima, Victor Ukleev, Atsushi Tsukazaki, Ryutaro Yoshimi, Minoru Kawamura, Kei Takahashi, Takayasu Hanashima, Kazuhisa Kakurai, Takahisa Arima, Masashi Kawasaki, Yoshinori Tokura Ferromagnetism in topological insulators could lead to exotic quantum phenomena such as quantum anomalous Hall effect. A predominant requirement for such phenomena is the formation of an exchange gap at the Dirac surface states, being realized not only by magnetic doping but also by proximitizing ferromagnetic insulators. Here, we report on the effective gap formation driven by proximity coupling via detection of large anomalous Hall conductivity in heterostructures consisting of ferromagnetic insulator Cr2Ge2Te6 and topological insulator (Bi,Sb)2Te3. While no discernible magnetization in the (Bi,Sb)2Te3 layer is probed by spinpolarized neutron reflectometry, the emergence of large anomalous Hall effect implies that the wavefunction of the Dirac surface state gains an exchange field by penetrating into the Cr2Ge2Te6 by approximately 23 nm, finally activating a large Berry curvature. The presently verified mechanism of strong ferromagnetic proximity effect paves a way to enrich the proximity coupling phenomena in versatile topological quantum materials. 
Thursday, March 7, 2019 12:51PM  1:03PM 
S02.00009: Anisotropic magnetotransport and planar Hall effect in the quantum anomalous Hall regime Michelle Tomczyk, Di Xiao, CuiZu Chang, Anthony R. Richardella, ChaoXing Liu, Nitin Samarth Perturbations to the metallic surface states of topological insulators (TIs) through interactions with magnetism or superconductivity can result in novel phenomena. For example, magneticallydoped TIs realize the theoreticallypredicted quantum anomalous Hall (QAH) insulator, in which the surface states are gapped while current is carried in quantized chiral edge states even in zero magnetic field. Understanding the transition between the QAH insulator and dissipative metallic conduction regimes is of fundamental importance. We study this transition by measuring electrical transport while rotating an external magnetic field in different planes relative to the surface. Using scaling plots of the Hall and longitudinal conductance, we find an equivalency in the phase transition created by either rotating the field in the perpendicular plane or by increasing the temperature. Additionally, the angledependent inplane transverse magnetoresistance, the planar Hall effect, exhibits anomalous behavior when perturbed by a small outofplane magnetic field. We interpret these observations in terms of the interplay between magnetization, dissipationfree chiral edge states, and dissipative surface states. 
Thursday, March 7, 2019 1:03PM  1:15PM 
S02.00010: Berry Phase Engineering in Magnetic Topological Insulator Heterostructures FEI Wang, Yifan Zhao, Di Xiao, Wenbo Wang, Jue Jiang, Ling Zhang, Weiwei Zhao, ChaoXing Liu, Weida Wu, Moses H. W. Chan, Nitin Samarth, CuiZu Chang

Thursday, March 7, 2019 1:15PM  1:27PM 
S02.00011: Magnetotransport and Magnetism in Antiferromagnetic GdSbTe TsungChi Wu, Akhilesh Singh, MingChin Chen, Raman Sankar, Fangcheng Chou, WeiLi Lee The crystal structure of GdSbTe belongs to the PbFCltype family that is known for exhibiting a possible topological nodalline phase. The spin7/2 Gd^{3+} ions form a square lattice in the ab plane with large moments. Recently, a Diraclike state was observed in GdSbTe by ARPES measurement [1]. Magnetization and specific heat measurements also revealed an antiferromagnetic (AFM) transition with a Néel temperature of around 12 K [2], making it a suitable system to study the interplay between AFM and topological states. Here, we report the angular dependence of the magnetotransport properties in GdSbTe. Several features in magnetoresistance (MR) measurements were uncovered while sweeping an inplane magnetic field, including abrupt increases of MR occurs at 2 T and 6 T and an unusual hysteretic giant magnetoresistance (GMR)like behavior at higher magnetic fields. We remark that those features are absent when the magnetic field is applied perpendicular to the abplane direction. The magnetotransport and magnetization measurements up to a magnetic field of 14 T will be presented and compared to several metallic spin systems. 
Thursday, March 7, 2019 1:27PM  1:39PM 
S02.00012: MagnetoTransport Study of Magnetic/Nonmagnetic Topological Insulator Heterostructures Di Xiao, Fei Wang, Run Xiao, Ling Zhang, Haizhou Lu, ChaoXing Liu, Moses H. W. Chan, CuiZu Chang, Nitin Samarth Breaking timereversal symmetry in a topological insulator (TI) by a magnetic perturbation can give rise to a variety of exotic quantum phenomena such as quantum anomalous Hall effect. Since the surface states of TIs have a spin helical massless Dirac structure, undoped TI films usually show weak antilocalization (WAL) quantum corrections to diffusive transport, characterized by a positive magnetoresistance (MR). Here, we fabricate magnetically doped TI films on pristine TI films with different thicknesses to form magnetic/nonmagnetic TI heterostructures and systematically study their magnetotransport properties. When the thickness of the TI layer is ≤2QL, the MR shows a typical butterfly shape due to domain wall scattering. However, when the thickness of the TI layer is ≥ 3QL, the MR is suppressed, similar to the WAL cusp, but near the magnetization reversal regime. We speculate that this “dip” in MR near the coercive field is a result of the coexistence of the gapless surface state of the TI layer and the ferromagnetic order in the magnetic TI layer. Our study provides new insights into magnetotransport phenomena in the presence of a superposition of gapped and gapless surface states. 
Thursday, March 7, 2019 1:39PM  1:51PM 
S02.00013: HoBi: The Effect of Magnetism on Extreme Magnetoresistance HungYu Yang, Jonathan Gaudet, Adam Aczel, David E Graf, Peter Blaha, Bruce Gaulin, Fazel Fallah Tafti

Thursday, March 7, 2019 1:51PM  2:03PM 
S02.00014: Neutron scattering study on a topological antiferromagnet Weiliang Yao, Yangmu Li, Kazuki Iida, Takashi Ohhara, Akiko Nakao, Barry L. Winn, John Tranquada, Igor Zaliznyak, Chenyuan Li, Chen Fang, Yuan Li As analogue of Dirac fermions in topological semimetals, magnon Dirac points have recently been proposed [1] and observed [2,3] in a threedimensional antiferromagnet, Cu3TeO6. Motivated by the expected presence of DzyaloshinskiiMoriya interactions in this system [1], we have performed a detailed magnetic neutron diffraction measurement on a single crystal, aiming to detect possible noncollinear spin arrangements in the magnetically ordered state. The result in turn allows for an estimate of the sizes of the topological nodal lines that are represented by the Dirac points in the U(1)symmetric approximation. Furthermore, we have attempted the first inelastic neutron scattering experiment in search of the putative topological magnon surface states [1,2]. 
Thursday, March 7, 2019 2:03PM  2:15PM 
S02.00015: Sign Reversal of the Anomalous Hall Effect in Magnetically Doped Topological Insulator Thin Films Yifan Zhao, Ling Zhang, Fei Wang, Jue Jiang, Moses H. W. Chan, CuiZu Chang Inducing magnetic orders in a topological insulator (TI) to break its time reversal symmetry has revealed many exotic topological quantum phenomena such as quantum anomalous Hall (QAH) effect. The QAH effect has been experimentally realized in the thin films of Cr and/or Vdoped (Bi,Sb)_{2}Te_{3}. The Vdoped Sb_{2}Te_{3}is one of two parent systems for the QAH state. Recently, we fabricated the Vdoped Sb_{2}Te_{3}films with varying V doping concentration and systematically studied their magnetotransport properties. We observed the sign reversal of the anomalous Hall (AH) effect in the V doped Sb_{2}Te_{3}films with increasing the V doping concentration. For low doping level, the sign of the AH effect is negative; When the V doping level reaches ~ 3% of Sb , the AH effect starts to show positive sign, consistent with that of the Vdoped QAH samples. The observation of the sign reversal of the AH effect in the Vdoped Sb_{2}Te_{3}films opens a new route to understand the interplay between the topological states and magnetism in magnetic doped TI films and facilitates the exploration of the underlying mechanism of the Vdoped QAH system. 
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