Bulletin of the American Physical Society
APS March Meeting 2020
Volume 65, Number 1
Monday–Friday, March 2–6, 2020; Denver, Colorado
Session L59: MnBi2Te4 and Related Compounds: Bulk Properties |
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Sponsoring Units: DMP Room: Mile High Ballroom 3C |
Wednesday, March 4, 2020 8:00AM - 8:12AM |
L59.00001: Anti-site disorder and competing magnetic ground states of Mn1-xSb2+0.67xTe4 Yaohua Liu, Xiaoping Wang, Jiaqiang Yan Intrinsic magnetic topological insulators (TIs) provide a fertile playground to pursuit exotic quantum states of matter at ambient conditions, such as the quantum anomalous Hall effect. MnBi2Te4, with the stacking of septuple-layers, has been recently predicted as the first instance of an antiferromagnetic TI, which has triggered intensive studies on related materials. The as-grown MnBi2Te4 is heavily electron-doped and substituting Bi with Sb is expected to fine-tune the Fermi level with little disturbance on the magnetic structure. Interestingly, we have found that the end compound MnSb2Te4, isostructural to MnBi2Te4 at room temperature, can host two dissimilar magnetic ground states with different magnetic wavevectors but similar ordering temperatures from magnetic measurements and single-crystal neutron diffraction (SCND) experiments. Energy-dispersive X-ray spectroscopy and SCND show Mn vacancies and Mn-Sb anti-site disorder in both cases. To explain the results, we consider a model where the sign of the effective inter-septuple-layer coupling becomes sensitive to the Mn-defect concentration on the Sb site. |
Wednesday, March 4, 2020 8:12AM - 8:24AM |
L59.00002: Native defects in Antiferromagnetic Topological Insulator MnBi2Te4 Zengle Huang, Jiaqiang Yan, Weida Wu The coupling of topological electronic states and magnetism can lead to various exotic phenomena such as quantum anomalous Hall effect, axion insulating state, etc. Recently, single crystals and thin films of MnBi2Te4 have been successfully synthesized and it has been shown to be a promising candidate of antiferromagnetic topological insulator [1, 2]. It is crucial to understand and control the defects in this material as they affect its electronic and magnetic properties. In this talk, I will present our study of the native defects in single-crystalline MnBi2Te4 using scanning tunneling microscopy (STM). We identify the dominant defects, MnBi antisites in the second layer of Bi, which may impact the magnetic properties of MnBi2Te4 [3, 4, 5]. In addition, we observe another interesting defects with pronounced defect states near the conduction band edge. |
Wednesday, March 4, 2020 8:24AM - 8:36AM |
L59.00003: Magnetism in MnBi2Te4 and related compounds Jiaqiang Yan, Andrew May, Michael McGuire, Yaohua Liu, Brian Sales MnBi2Te4 has been extensively investigated recently as the first intrinsic antiferromagnetic topological insulator. This compound also shows a strong correlation between structural, magnetic, and transport properties. In this talk, I will present our work on how the stacking of septuple (MnBi2Te4) and quintuple (Bi2Te3) layers, chemical doping, high pressure, and antisite defects affect the magnetic properties. I will also discuss how these results can guide us fine-tuning the magnetism for desired topological phenomena. |
Wednesday, March 4, 2020 8:36AM - 8:48AM |
L59.00004: MnBi2nTe3n+1: from intrinsic antiferromagnetic to ferromagnetic topological insulators Ni Ni Magnetic topological insulators provide an important materials platform to explore emergent quantum phenomena. Recently, MnBi2Te4 was discovered to be the first material realization of a van der Waals (vdW) antiferromagnetic topological insulator (TI). In the two-dimensional (2D) limit, at a record high temperature of 4.5 K, MnBi2Te4 manifests the QAH effect in the forced ferromagnetic state above 12 T [1]. To realize the QAH effect at lower fields or even zero field, it is essential to search for ferromagnetic TIs or antiferromagnetic TIs with lower saturation fields. By reducing the interlayer magnetic exchange interaction through our rational design of the natural heterostructure consisting of the building blocks of [MnBi2Te4] septuple layers and [Bi2Te3] quintuple layers, I will show that this family of materials can be tuned from antiferromagnetic to ferromagnetic, providing a superior material platform to investigate various emergent phenomena arising from the interplay between magnetism and band topology [2,3]. |
Wednesday, March 4, 2020 8:48AM - 9:00AM |
L59.00005: Ferromagnetic van der Waals compound MnSb1.8Bi0.2Te4 Yangyang Chen, Ya-Wen Chuang, Seng Huat Lee, Yanglin Zhu, Kevin Honz, Yingdong Guan, Yu Wang, Ke Wang, Zhiqiang Mao, Colin Heikes, Patrick Quarterman, Pawel Zajdel, Julie Ann Borchers, William Ratcliff, Jun Zhu The coexistence of topology and magnetism in the same material offers the possibility to realize novel quantum phenomena such as the quantum anomalous Hall effect. Van der Waals magnetic compounds in the form of MnSbxBi2-xTe4 are promising candidates. In this work, we show that a Sb-rich composition MnSb1.8Bi0.2Te4 exhibits a ferromagnetic ground state below a Curie temperature of 26 K, in contrast to antiferromagnetic states found in previous studies of this compound family. Magneto-transport measurements are performed on flakes that are ~ 100 nm thick and prepared in an argon atmosphere. At low temperature, pronounced hysteresis is observed in magnetic field sweeps of Rxy and Rxx. A remnant magnetization of M0 = 0.6 μB/Mn, is extracted from bulk magnetization measurements. The presence of a major ferromagnetic phase is further confirmed by neutron diffraction studies. An excess signal beyond the conventional anomalous Hall effect is observed at T < 12 K. We discuss the implications of our results. |
Wednesday, March 4, 2020 9:00AM - 9:12AM |
L59.00006: Stability subtlety of layered magnetic topological insulator MnBi2Te4 Jinliang Ning, Yanglin Zhu, Zhiqiang Mao, Jianwei Sun Ab initio description of two dimensional magnetic materials (2DMM) thermodynamics faces great challenges, due to the coexistence of different kinds of chemical bonding, as well as coupling between charge, lattice, and spin degrees of freedom. As an illustration of such challenges, we investigated the metastability of a layered magnetic material MnBi2Te4, which hosts the intrinsic quantum anomalous Hall effect but the crystal itself is hard to synthesize. We calculated the reaction free energy of Bi2Te3+MnTe→MnBi2Te4, considering electron, vibration and magnetic contributions based on state-of-the-art SCAN+rVV101 total energy calculations. We found MnBi2Te4 to be stable only within a short high temperature range, consistent with experiments. Fundamental interactions including SOC effect, vdW interaction, 2D weak magnetism and lattice vibration all contribute subtly to the high-temperature stability of MnBi2Te4, which exemplify that interplay of topology and magnetism can contribute to the stability of the material hosting it. These findings and methods pave a way for future high throughput discovery of novel 2DMM. |
Wednesday, March 4, 2020 9:12AM - 9:24AM |
L59.00007: Magnetic structure evolution in the Mn(Bi,Sb)2Te4 family of intrinsic magnetic topological insulators Colin Heikes, Patrick Quarterman, Yangyang Chen, Ya-Wen Chuang, Seng Huat Lee, Yanglin Zhu, Kevin Honz, Yingdong Guan, Yu Wang, Ke Wang, Zhiqiang Mao, Jun Zhu, Pawel Zajdel, Julie Ann Borchers, William Ratcliff The Mn(Bi,Sb)2Te4 family of intrinsic magnetic topological insulators has been predicted to be an ideal platform to realize a high temperature quantum anomalous Hall state, an axion insulating state, as well as a variety of other non-trivial band topologies. The strong coupling between the magnetic ordering in these compounds and the details of their band structure makes understanding their magnetic structure and its evolution with chemistry and magnetic field critical for understanding these exotic states. Our prior work has demonstrated that the field driven spin canting in MnBi2Te4 drives the measured intrinsic anomalous Hall effect in that compound but there are many questions to be addressed about the details of the evolution of the magnetic phase diagram in this system as the Bi atoms are replaced with Sb [1]. Prior magnetometry and magnetotransport shows a clear bulk magnetic behavior change with increased Sb content, but the microscopic details of this evolution are unclear [2]. We will present structural and magnetic neutron scattering measurements and other magnetic characterization of the Mn(Bi,Sb)2Te4 family of compounds to clarify this evolution. |
Wednesday, March 4, 2020 9:24AM - 9:36AM |
L59.00008: Single Crystal Study of Magnetic Topological Material MnBi2xTe3x+1. Joshua Wakefield, Takashi Kurumaji, Takehito Suzuki, Joseph G Checkelsky MnBi2Te4 has emerged as the first stoichiometric antiferromagnetic topological insulator [1]. In thin flakes, MnBi2Te4 has shown remarkable properties including the quantum anomalous Hall (QAH) effect [2]. We investigate the single crystal growth and transport properties of other members of the MnBi2xTe3x+1 family and find both temperature and low field dependent crossovers from A-type antiferromagnetism to ferromagnetism in MnBi4Te7, suggesting MnBi4Te7 as another candidate for QAH effects in zero external field. We discuss the anomalous Hall response in relation to the magnetic structure, and dependence of the transport properties on angle of the external magnetic field. |
Wednesday, March 4, 2020 9:36AM - 9:48AM |
L59.00009: Crystal and magnetic structure of magnetic topological insulators MnBi2nTe3n+1 LEI DING, Chaowei Hu, Feng Ye, Erxi Feng, Ni Ni, Huibo Cao We present a systematic investigation of the crystal structure and magnetism of van der Waals topological insulators MnBi2nTe3n+1 (n = 1, 2) using single-crystal neutron diffraction, where emergent quantum phenomena have been recently observed. We show unambiguously that MnBi2Te4 orders antiferromagnetically below 24 K featured by a magnetic symmetry RI-3c while MnBi4Te7 is antiferromagnetic below 13 K with a distinct magnetic space group Pc-3c1. They both present antiferromagnetically coupled ferromagnetic layers with spins along the c-axis. Further, we put forward a stacking rule for the crystal structure of an infinitely adaptive series MnBi2nTe3n+1 with the building unit of [Bi2Te3]. This enables us to draw that a two-dimensional magnetism limit might be realized in the derivatives. Our work may promote the theoretical predictions of exotic quantum states in the series of MnBi2nTe3n+1. |
Wednesday, March 4, 2020 9:48AM - 10:00AM |
L59.00010: Large intrinsic anomalous Hall effect in hole-doped ferromagnetic phase MnSbxBi2-xTe4 Seng Huat Lee, Yanglin Zhu, Lujin Min, Verlinde Katrina, Jingyang He, David E Graf, Ronald Redwing, Zhiqiang Mao MnBi2Te4, an intrinsic magnetic topological insulator, has recently been predicted to possess a variety of topological quantum states, including quantum anomalous Hall insulator, axion insulator in its 2D thin layers and an ideal Weyl semimetal state in its bulk ferromagnetic (FM) phase1,2. Although several interesting properties, including Chern insulator, axion insulator, and anomalous Hall effect (AHE) in its canted antiferromagnetic phase have been observed, the predicted FM Weyl state remains elusive3-5. In this talk, we will report our magnetotransport studies on MnSbxBi2-xTe4. We will show when the Sb concentration is tuned to be close to a critical concentration where carrier density reaches a minimum, the FM phase under a high field range exhibits a large intrinsic AHE with the anomalous Hall angle reaching 5%. Moreover, the carrier mobility also reaches a maximum at the critical concentration. All these features are possibly associated with the long-sought ideal Weyl state. |
Wednesday, March 4, 2020 10:00AM - 10:12AM |
L59.00011: Quantum Oscillations in Intrinsic Magnetic Topological Insulator MnBi2-xSbxTe4 Qianni Jiang, Zaiyao Fei, Tiancheng Song, Jiaqiang Yan, Paul Malinowski, Zhaoyu Liu, David E Graf, Xiaodong Xu, Jiun-Haw Chu The recently discovered first intrinsic antiferromagnetic (AFM) topological insulator (TI) MnBi2Te4 is expected to possess various exotic quantum states including axion insulator and quantum anomalous Hall effect. The band structure portrayed by ARPES measurements reveals nontrivial topology, but claims regarding the surface states are still controversial. When Bi is substituted by Sb, the material crosses a bulk charge neutrality point, from being electron-doped to hole-doped. By applying a magnetic field, it is possible to realize a magnetic Weyl semimetal phase by switching the AFM phase to the FM phase through a meta-magnetic transition at B ~ 6T. Here, we present Shubnikov–de Haas oscillations of both electron and hole-doped MnBi2-xSbxTe4 in the FM state and trace its evolution as a function of chemical doping, providing the first measurement of the band structures of MnBi2-xSbxTe4 in the FM state. |
Wednesday, March 4, 2020 10:12AM - 10:24AM |
L59.00012: Optimization of the intrinsic magnetic topological insulator MnBi2Te4 and transport study Fengqi Song Magnetic topological insulators (MTIs) offer a combination of topologically nontrivial characteristics and magnetic order and show promise in terms of potentially interesting physical phenomena such as quantum anomalous Hall (QAH) effect. However, the understanding of their properties and potential applications have been limited due to a lack of suitable MTIs. Here, we grow single crystals of Mn(Sb,Bi)2Te4 to search for intrinsic MTIs. We perform angle-resolved photoemission spectroscopy, transport measurements, and first-principles calculations to investigate the band structure, transport properties, and magnetism, as well as the evolution of their topological properties. We find that there exists an optimized MTI zone in the Mn(Sb,Bi)2Te4 phase diagram, which could possibly host a high-temperature QAH phase. We also report the reserved anomalous Hall effect (AHE) in the MnBi2Te4 thin film. By employing the top/bottom gate, a negative AHE loop gradually decreases to zero and changes to a reversed sign. The reversed AHE exhibits distinct coercive fields and temperature dependence from the previous AHE. It reaches the maximum inside the gap of the Dirac cone. The reversed AHE is attributed to the competition of intrinsic Berry curvature and extrinsic skew scattering. |
Wednesday, March 4, 2020 10:24AM - 10:36AM |
L59.00013: Magnetotransport properties in MnBi2nTe3n+1 Chaowei Hu, Jinyu Liu, Scott Mackey, Ni Ni Recently, magnetic topological insulators MnBi2nTe3n+1 were discovered, where quantized anomalous hall resistance was observed in the two-dimensional limit of MnBi2Te4 at a record high temperature of 4 K under 12 T, providing an important material platform to explore emergent quantum phenomena such as quantized anomalous Hall effect and Majorana modes, etc. MnBi2nTe3n+1 family is made of alternating one septuple [MnBi2Te4] and (n-1) quintuple [Bi2Te3] layers, where the interlayer magnetic couplings are tuned systematically with increasing n. In this talk, we will show our recent results on the magentotransport properties in MnBi2nTe3n+1, shedding light on the interplay between magnetism and band topology. |
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L59.00014: Intrinsic magnetic topological states in MnBi2Te4 family Jing Wang Here, we first predict the tetradymite-type compound MnBi2Te4 and its related materials host topologically nontrivial magnetic states. The magnetic ground state of MnBi2Te4 is an antiferromagetic topological insulator state with a large topologically non-trivial energy gap (0.2 eV). It presents the axion state, which has gapped bulk and surface states, and the quantized topological magnetoelectric effect. It has several advantages over the previous proposals on realizing the topological magnetoelectric effect. The intrinsic magnetic and band inversion further lead to quantum anomalous Hall effect in odd layer MnBi2Te4 thin film with combined inversion and time-reversal symmetry breaking, which has been recently observed in experiments. The high quality intrinsic MnBi2Te4 together with other magnetic/superconducting 2D materials provides fertile ground for exploring exotic topological quantum phenomena. |
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L59.00015: Pressure-tuned interlayer coupling of the magnetic topological insulators MnBi2Te4(Bi2Te3)n (n=1,2) Jifeng Shao, Xiao-Ming Ma, Jingyuan Li, Yichen Sun, Rui'e Lu, Meng Zeng, Yujie Hao, Chang Liu, Qihang Liu, Yue Zhao
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