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 J52: Magnetic Topological Materials 2:Mn-Bi-TeLive
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Sponsoring Units: DMP GMAG Chair: Dmitry Ovchinnikov, University of Washington |
Tuesday, March 16, 2021 3:00PM - 3:12PM Live |
J52.00001: Intertwined Topological and Magnetic Orders in Atomically Thin Chern Insulator MnBi2Te4 Dmitry Ovchinnikov, Xiong Huang, Zhong Lin, Zaiyao Fei, Jiaqi Cai, Tiancheng Song, Minhao He, Qianni Jiang, Chong Wang, Hao Li, Yayu Wang, Yang Wu, Di Xiao, Jiun-Haw Chu, Jiaqiang Yan, Cui-Zu Chang, Yongtao Cui, Xiaodong Xu The interplay between band topology and magnetic order plays a key role in new quantum states of matter. MnBi2Te4, a crystalline topological van der Waals magnet, has recently emerged as an exciting platform for exploring Chern insulator physics. Its layered antiferromagnetic ground state was predicted to enable even-odd layer-number dependent topological states, while tunability of spin states via external magnetic field offers an interesting venue for observation of topological phase transitions. In this work by combination of magnetic circular dichroism, transport, and microwave impedance measurements (MIM) we investigate connection between bulk electronic structure, topological order, and magnetic states in thin flakes of MnBi2Te4. We establish one to one correspondence between spin state and Chern number in this material and observe band crossing, which is closing and reopening of bulk bandgap as a function of external magnetic field. Furthermore, we investigate Chern gap formation in MnBi2Te4 and its evolution as a function of temperature. Finally, we will discuss even-odd layer-number dependent effects on bulk electronic structure of MnBi2Te4 and Chern insulator state formation. |
Tuesday, March 16, 2021 3:12PM - 3:24PM Live |
J52.00002: Quantum Oscillations in the Field-Induced Ferromagnetic State of MnBi2-xSbxTe4 Qianni Jiang, Chong Wang, Paul Malinowski, Zhaoyu Liu, Yue Shi, Zhong Lin, Zaiyao Fei, Tiancheng Song, David E Graf, Shalinee Chikara, Xiaodong Xu, Jiaqiang Yan, Di Xiao, Jiun-Haw Chu The intrinsic antiferromagnetic (AFM) topological insulator (TI) MnBi2Te4 is expected to possess various exotic quantum states including axion insulator and quantum anomalous Hall effect. 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 MnBi2-xSbxTe4 in a wide range of Sb concentrations close to the charge neutrality point (0.33 ≤ x ≤ 1.21) in the FM state. The evolution of the oscillation frequency and the effective mass shows a good agreement with the Weyl semimetal band-structure of ferromagnetic MnBi2Te4 predicted by density functional calculations. Intriguingly, the quantum oscillation frequency shows a strong temperature dependence, indicating that the electronic structure sensitively depends on magnetism. |
Tuesday, March 16, 2021 3:24PM - 3:36PM Live |
J52.00003: Ferromagnetic MnSb2Te4: A p-type topological insulator with magnetic gap closing at high Curie temperatures of 45-50 K Oliver Rader, S. Wimmer, J. Sánchez-Barriga, P. Küppers, A. Ney, Enrico Schierle, F. Freyse, O. Caha, J. Michalicka, M. Liebmann, D. Primetzhofer, M. Hoffmann, A. Ernst, Mikhail Otrokov, Gustav Bihlmayer, Eugen Weschke, Bella A C I Lake, Eugene V. Chulkov, Markus Morgenstern, Guenther Ernst Bauer, G. Springholz Mn enables the formation of intrinsic magnetic topological insulators for the quantum anomalous Hall effect with A1B2C4 stoichiometry, e. g., antiferromagnetic MnBi2Te4 with 25 K Néel temperature. Here, we show that p-type MnSb2Te4, previously considered topologically trivial, is a ferromagnetic topological insulator with high Curie temperature of 45 to 50 K. It displays out-of-plane magnetic anisotropy, the nontrivial topology is robust in band structure calculations towards magnetic disorder, provides a Dirac point of the topological surface state close to the Fermi level with out-of-plane spin polarization in spin-ARPES, and exhibits a magnetically induced band gap of 17 meV that closes at the Curie temperature as demonstrated by scanning tunneling spectroscopy. Moreover, it displays a critical exponent of magnetization β≈1, indicating the vicinity of a quantum critical point. We identify the influences of structural and magnetic disorder that render MnSb2Te4 the ideal system for tuning electric and magnetic properties of quantum anomalous Hall systems. |
Tuesday, March 16, 2021 3:36PM - 3:48PM Live |
J52.00004: Coexistence of a Gapless Topological State and Surface Ferromagnetism in MnBi2Te4 Daniel Nevola, Haoxiang Li, Jiaqiang Yan, Robert G Moore, Ho Nyung Lee, Hu Miao, Peter David Johnson The recent discovery of the intrinsic magnetic topological insulator MnBi2Te4 has sparked considerable interest because of the novel quantum properties that can arise as a result of the coupling between the topological and magnetic properties. However, the inability of the magnetic ordering to open a gap at the Dirac point, in contradiction to theoretical calculation, has led to speculation as to whether the magnetic ordering extends to the surface region. We use both static and time resolved ARPES to show that bulk magnetism does extend to the surface of MnBi2Te4. Our results have important implications for understanding the fundamental properties of the topological state and offer a clue for understanding its low quantum anomalous hall temperature. |
Tuesday, March 16, 2021 3:48PM - 4:00PM Live |
J52.00005: Absence of Correlation Between Carrier Type and Magnetic Properties of MnBi2Te4 Kerrie Koller, Seul-Ki Bac, Xinyu Liu, Logan Riney, Jiashu Wang, William Powers, Maksym Zhukovskyi, Tatyana Orlova, Malgorzata Dobrowolska, Jacek Furdyna, Badih A Assaf MnBi2Te4 is an intrinsic magnetic topological material; this makes MnBi2Te4 ideal for exotic quantum phenomena, such as the anomalous Hall effect, axion electrodynamics, and anomalous Nernst effect [1]. In addition, MnBi2Te4 is applicable to detect and manipulate the magnetization in data storage devices using various magneto-electrical routes. Here we investigate the magnetic properties of MnBi2Te4 samples with n-type and p-type carriers grown by molecular beam epitaxy. We used SQUID magnetometry to measure the magnetization as a function of field and temperature and to extract the magnetic properties MS and TC. When compared to the carrier type of the samples, we find that there is no correlation between the carrier type and the magnetic properties MS, and TC, unlike in the case of magnetic semiconductors. This independence indicates that MnBi2Te4 becomes magnetic as a result of a direct exchange interaction. |
Tuesday, March 16, 2021 4:00PM - 4:12PM Live |
J52.00006: Neutron diffraction study of magnetism in van der Waals layered MnBi2nTe3n+1 LEI DING, Chaowei Hu, Erxi Feng, Miaofang Chi, Ni Ni, Huibo Cao We present a systematic investigation of the crystal structure and magnetism of MnBi2nTe3n+1 (n = 1, 2, 3, 4) which have been recently found to be intrinsic magnetic topological insulators. Neutron diffraction unveils that considerable Bi atoms occupy at the Mn sites while no detectable magnetic Mn occupies at non-magnetic sites in all the cases. The occupancy of Mn monotonically decreases with the increase of n. Polarized neutron diffraction on MnBi4Te7 reveals that its magnetization density is obviously accumulated at the Mn site, corroborating the distribution of the chemical defects. We suggest that the site defects but not site mixings are inherent and should be a common mark to this family. Our work provides material-specified structural parameters that may be useful for band structure calculations to understand the observed topological surface states and for designing quantum magnetic materials through chemical doping. |
Tuesday, March 16, 2021 4:12PM - 4:24PM Live |
J52.00007: Giant photogalvanic effect and second-harmonic generation in magnetic axion insulators Ruixiang Fei, Wenshen Song, Li Yang Combining quantum perturbation theory and first-principles simulation, we predict giant nonlinear optical responses (NLOs) in even septuple layers of MnBi2Te4 family materials (MBTs), which are the zero-plateau quantum anomalous Hall systems (QAHs). The interlayer antiferromagnetic order breaks the inversion symmetry, and the amplitudes of injection current and second harmonic generation can be about one order of magnitude larger than those of the ferroelectrics, such as LiNbO3 and BiFeO3. Moreover, unlike the injection current in ferroelectrics, we find that the injection photocurrent only emerges under a linearly polarized light in MBTs. Our analysis indicates that these giant linearly-polarized second-order NLOs are resulted from the parity-time symmetry, three-fold rotation symmetry, and large spin-orbit coupling. These enhanced NLOs are valuable for characterizing subtle magnetic orders in QAHs and shed light on photo-detecting and photovoltaic applications based on emerging magnetic topological materials. |
Tuesday, March 16, 2021 4:24PM - 4:36PM Not Participating |
J52.00008: Magnetic structure evolution of 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 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 about the details of the evolution of magnetic phase diagram in this system as the Bi atoms are replaced with Sb. Prior magnetometry and magnetotransport shows a clear bulk magnetic behavior change with increased Sb content, but the microscopic details of this evolution are unclear. 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. |
Tuesday, March 16, 2021 4:36PM - 4:48PM Live |
J52.00009: Switching on ferromagnetic coupling by Mn/Sb antisite disorder in Mn(Bi1-xSbx)4Te7 Chaowei Hu, Scott Mackey, Ni Ni The fine control of magnetism in topological magnetic materials is crucial since the interplay between magnetism and band topology can lead to exotic emergent phenomena, such as quantum anomalous Hall effect, etc. We present a continuous control of the interlayer magnetic coupling in the newly-discovered intrinsic topological insulator MnBi4Te7 by Sb-doping. Through the transport and thermodynamic measurements, it is revealed how the system evolves from antiferromagnetic to ferromagnetic and then ferrimagnetic. We attribute this evolution to the formation of the Mn/Sb antisite disorder which not only leads to the magnetic dilution effect, but also results in extra Mn2/Mn3 magnetic sublattices which act as a switch for dominant Mn1 sublattice in MnBi4Te7 to go from antiferromagnetic to ferromagnetic. Therefore, our work provides a system with continuous tuning of the delicate magnetic energy scales in an intrinsic topological insulator and demonstrates defect control as an efficient strategy toward the magnetic control in the system. |
Tuesday, March 16, 2021 4:48PM - 5:00PM Live |
J52.00010: Strongly Gapped Topological Surface States in MnBi2Te4(Bi2Te3)n Family Kyle Gordon, Chaowei Hu, Hongyi Sun, Garrison Linn, Bryan Berggren, Tay-Rong Chang, Qihang Liu, Ni Ni, Daniel Dessau The MnBi2Te4(Bi2Te3)n family of materials are potential candidates for magnetic topological insulators (MTIs) that may show the Quantum Anomalous Hall Effect (QAHE). This class of materials are heterostructures of MnBi2Te4 and Bi2Te3 layers that are stacked together via van der Waals forces, with n number of Bi2Te3 layers interstitially placed between MnBi2Te4 layers. In this talk, we present Angular Resolved Photoemission Spectroscopy (ARPES) experiments on MnBi4Te7, MnBi6Te10, and MnBi8Te13, demonstrating the topological nature of each material. Furthermore, we deconvolve the surface spectra due to each possible surface termination for each stacking arrangement, demonstrating a rich transition from the gapless MnBi2Te4 surface, through a gapped Bi2Te3-like surface, and ending with an approximate pure Bi2Te3 surface. |
Tuesday, March 16, 2021 5:00PM - 5:12PM Live |
J52.00011: Magnetic topological properties of MnBi2Te4 tuned by electric coupling Wei Luo, Maohua Du, Fernando A Reboredo, Mina Yoon Using first-principle calculations, we investigate the electronic, magnetic and quantum topological properties of a multilayer MnBi2Te4 system on substrates. We propose a mechanism to control its electronic, magnetic and topological properties by electric field. We identify the most stable stack order between MnBi2Te4 and the substrates. Due to the strong coupling between the magnetic moments and the electrical dipole moments of the substrate, the magnetic order of MnBi2Te4 changes drastically by applying an electric field, which also leads to a topological phase transition. Our work proposes a new way to control the magnetic order of MnBi2Te4 and its topological states by electric fields. |
Tuesday, March 16, 2021 5:12PM - 5:24PM Live |
J52.00012: Electronic structure and magnetic properties of MnBi2Te4 and MnSb2Te4 Yongbin Lee, Robert J McQueeney, Liqin Ke Using ab initio methods and atomic spin dynamics, we investigate the electronic structure and magnetism in MnBi2Te4 and MnSb2Te4. By comparing the bandstructure obtained using DFT+U and Quasi-particle self-consistent GW methods, we found that a U≈ 5 eV Hubbard correction on Mn-d orbitals is needed to describe the electronic structure and magnetic ordering better with DFT+U. We also investigate the intrinsic magnetic properties in these compounds, including exchange couplings and magnetocrystalline anisotropy. The anti-site defects are found to form more easily in MnSb2Te4 than in MnBi2Te4, creating antiferromagnetic Mn-Mn couplings within the septuple block. We investigate the origin of anisotropy and the effects of dimensionality, anti-site defects, and interlayer ordering on anisotropy. Our calculated results are in reasonable agreement with the recent experiments. We also discuss the origin of non-hysteretic spin-flop behavior in these compounds. |
Tuesday, March 16, 2021 5:24PM - 5:36PM Live |
J52.00013: Coupling of topology and magnetic ordering in Axion Insulator and Weyl semimetal phases of MnB2X4 (A = Sb, Bi; X = Se, Te) Sugata Chowdhury, Kevin Garrity, Amber McCreary, Angela Hight Walker, Francesca Tavazza Axion insulators have been the subject of enormous interest because these materials can carry spin-polarized edge states even in the absence of an external magnetic field. Our calculations reveal that the ferromagnetic phase of bulk MnB2X4 (B = Sb, Bi; X=Se, Te) is either a nodal line or Weyl semimetal, depending on the direction of the spins. In the ground state antiferromagnetic phase, they instead become antiferromagnetic topological insulators, a type of Axion insulator. The intrinsic time reversal symmetry breaking at the surface of MnB2X4 removes the Dirac cone feature seen in typical topological insulators, allowing the observation of the half-integer quantum anomalous Hall effect (QAHE). We find that the direction of magnetic moment and the magnetic properties depend on the choice of chalcogenide, while the choice of B atom modifies the amount of band inversion. These stoichiometric magnetic materials are excellent candidates for spintronic devices. We also, investigated vibrational properties of all these materials to understand the how chemical substitutions effect the optical properties of the materials. |
Tuesday, March 16, 2021 5:36PM - 5:48PM Live |
J52.00014: Experimental evidence of the field-induced Weyl state in Mn(Bi1-xSbx)2Te4 Seng Huat Lee, David E Graf, Yanglin Zhu, Hemian Yi, Samuel Ciocys, Eun Sang Choi, Rabindra Basnet, Arash Fereidouni, Aaron Wegner, Yifan Zhao, Lujin Min, Katrina Verlinde, Jingyang He, Ronald Dean Redwing, Venkatraman Gopalan, Hugh O. H. Churchill, Alessandra Lanzara, NITIN SAMARTH, Cui-Zu Chang, 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 (QAHI), axion insulator in its 2D thin layers, and an ideal Weyl semimetal state in its bulk ferromagnetic (FM) phase1-3. QAHI and axion insulator in MnBi2Te4 thin layers have been experimentally demonstrated4,5, but the predicted FM Weyl state remains elusive. In this talk, we report the experimental evidence of the field-induced Weyl state in Mn(Bi1-xSbx)2Te46. The characteristics of the expected Weyl state were observed when the system is tuned to be lightly hole-doped via Sb substitution for Bi and is manifested by a field-driven electronic phase transition as well as large intrinsic anomalous Hall effect in the FM phase. Our results establish a promising platform for exploring the physics underlying the long-sought, ideal TRS breaking type-II WSM. |
Tuesday, March 16, 2021 5:48PM - 6:00PM On Demand |
J52.00015: Analytical solution to the surface states of antiferromagnetic topological insulator MnBi2Te4 Hai-Peng Sun, Chunming Wang, Songbo Zhang, Rui Chen, Haizhou Lu, X. C. Xie Recently, the intrinsic magnetic topological insulator MnBi2Te4 has attracted great attention. It has an out-of-plane antiferromagnetic order, which is believed to open a sizable energy gap in the surface states. This gap, however, was not always observable in the latest ARPES experiments. To address this issue, we analytically derive an effective model for the 2D surface states by starting from a 3D Hamiltonian for bulk MnBi2Te4 and taking into account the spatial profile of the bulk magnetization. We suggest that the the diminished surface gap in the recent experiments may be caused by a much smaller and more localized intralayer ferromagnetic order. In addition, we calculate the spatial distribution and penetration depth of the surface states, which are mainly embedded in the first two septuple layers from the terminating surface. From our analytical results, the influence of the bulk parameters on the surface states can be found explicitly. Furthermore, we derive a k.p model for MnBi2Te4 thin films and show the oscillation of the Chern number between odd and even septuple layers. Our results will be helpful for the ongoing explorations of the MnBixTey family. |
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