Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session S43: Tunable Magnetic Topological InsulatorsFocus
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Sponsoring Units: DMP Chair: Tong Zhou, University at Buffalo Room: Room 317 |
Thursday, March 9, 2023 8:00AM - 8:12AM |
S43.00001: Quantum metric nonlinear Hall effect in a topological antiferromagnetic heterostructure Anyuan Gao, Suyang Xu The geometrical properties of electron Bloch wavefunctions are central to modern condensed matter physics. In particular, the studies of Berry curvature have led to countless breakthroughs, ranging from the quantum Hall effect in 2DEGs to the anomalous Hall effect in ferromagnets. Hence, an important open question is to search for quantum geometrical phenomena beyond Berry curvature. This is possible since Berry curvature is only the imaginary component of quantum geometry. By contrast, the real component is known as a quantum metric, which has been rarely explored and responses from quantum metric have remained largely missing. By interfacing even-layered MnBi2Te4 (a PT-symmetric antiferromagnet (AFM)) with black phosphorus, we observe a new nonlinear Hall current, which switches direction upon reversing the AFM spins and exhibits distinct scaling that suggests a non-dissipative nature. This antiferromagnetic nonlinear Hall response arises from the dipole moment of the quantum metric. Like the anomalous Hall effect brought Berry curvature under the spotlight, our results open the door to discovering manifestations of the quantum metric. Our observation bridges nonlinear electronics with AFM spintronics, suggesting intriguing possibilities such as using AFM spins to harvest electromagnetic radiation energies. |
Thursday, March 9, 2023 8:12AM - 8:24AM |
S43.00002: Strain engineering of quantum geometry in magnetic topological insulators Barun Ghosh, Sugata Chowdhury, Tay-Rong Chang, Hsin Lin, Bahadur Singh, Suyang Xu, Arun Bansil Quantum metric, the real part of the quantum geometric tensor, is an important but often overlooked aspect of the Bloch wavefunction. The PT (P=inversion, T=time reversal ) symmetric magnets, which naturally suppress the Berry curvature-induced anomalous Hall effect, are suitable candidates for exploring the quantum metric-induced effects. Using density functional theory based ab initio calculations and low energy models, we explore the quantum metric dipole-induced intrinsic non-linear Hall effect (INHE) in MnBi$_{2n}$Te$_{3n+1}$ thin films. By applying uniaxial strain along various directions of the crystal structure, we break the threefold rotational symmetry and predict the existence of large INHE (~mA/V$^2$) in this family of materials. We show that INHE has large values near the band anti-crossing points, and it strongly depends on the strain and the Neel vector orientation. Our work promotes the MnBi$_{2n}$Te$_{3n+1}$ series of compounds as an exciting material platform for exploring and engineering various quantum geometry-induced effects. |
Thursday, March 9, 2023 8:24AM - 8:36AM |
S43.00003: Magnetic photocurrent in even-layered topological antiferromagnet MnBi2Te4 Zumeng Huang, Zhe Sun, Anyuan Gao, Tiema Qian, Siyuan Ding, Jian Tang, Kenji Watanabe, Takashi Taniguchi, Ni Ni, Suyang Xu, Qiong Ma MnBi2Te4 is a magnetic topological insulator that holds rich physical properties down to their 2D limit. Each septuple layer consists of a Bi2Te3 layer and a MnTe layer, which give rise to its topology and pristine magnetism, respectively. Moreover, as the magnetic moments couple antiferromagnetically between adjacent septuple layers, the spin texture breaks the inversion symmetry of even-layered MnBi2Te4 and leads to magnetic photocurrents that have been rarely studied before. In this talk, I will present our experimental study of the optoelectronic responses in even-layered MnBi2Te4. We observe an intrinsic photocurrent that can be controlled by external electrical and magnetic fields. I will also discuss how the magnetic photocurrent could also decode MnBi2Te4’s quantum geometrical structures. |
Thursday, March 9, 2023 8:36AM - 9:12AM |
S43.00004: Magnetic-Field induced Weyl State in Intrinsic Magnetic Topological Insulator MnBi2nTe3n+1 Invited Speaker: Seng Huat Lee Recent discoveries of intrinsic magnetic topological insulators have generated immense interest since they can generate various topological quantum states, such as quantum anomalous Hall insulators, axion insulators, and Weyl semimetal. In this talk, I will present our recent studies on intrinsic magnetic topological insulators MnBi2nTe3n+1 [1-4]. I will first report on our discoveries of the field-induced ideal Weyl state in MnBi2Te4 [2]. Through fine chemical potential tuning by Sb substitution for Bi, we have observed transport evidence of a long-sought topological state – an ideal type-II ferromagnetic (FM) Weyl state with one pair of Weyl nodes in the lightly hole-doped samples. Their transport signatures of the Weyl state are manifested by a field-driven electronic structure transition, a negative longitudinal magnetoresistance attributable to the chiral anomaly, as well as a large intrinsic anomalous Hall effect in the FM phase. Furthermore, we also revealed a giant spin-valve effect in the lightly electron-doped samples, sharply contrasted with the chiral anomaly behavior observed in the lightly hole-doped samples, which indicates Weyl fermions are not susceptible to magnetic scattering [3]. Finally, I will also discuss the possibility of the Weyl state driven by spontaneous ferromagnetism in heterostructural compounds Mn(Bi1-xSbx)2nTe3n+1 with n = 2 & 3. |
Thursday, March 9, 2023 9:12AM - 9:24AM |
S43.00005: Theoretical modeling of magnetic phase evolution in bulk n[Bi2Te3] x MnBi2Te4 Jalen Garner, Barun Ghosh, Kevin F Garrity, Deepti Jain, Bryan S Berggren, Daniel S Dessau, Seongshik Oh, Sugata Chowdhury The concept of electronic topology and the associated exotic states in quantum materials (QMs), such as the family of MnBi2Te4 (MBT), brings an excellent opportunity for developing next-generation nanodevices, especially those requiring high quantum mechanical coherence properties. MBT is an intrinsic antiferromagnetic topological insulator and displays Quantum Anomalous Hall Effect. This form of MBT requires a large magnetic field to present ferromagnetism; however, it has been discovered that this can be remedied by adding (n)Bi2Te3 quintuple layers to the system. A new experiment has also found phase transitions from antiferromagnetic states to ferromagnetic to paramagnetic, with each transition related to the bulk thickness of Bi2Te3. In this work, we use density functional theory (DFT) to observe how differences in energies and band structure reveal antiferromagnetic to ferromagnetic to nonmagnetic phase transitions of n[Bi2Te3] x MnBi2Te4 (nMBT) derivative compounds. In addition, we plan to present differences between slab surface state structures and bulk structures and each form’s resulting impact on the nMBT derivatives’ electronic and magnetic properties. |
Thursday, March 9, 2023 9:24AM - 9:36AM |
S43.00006: Tunable magnetism, charge carrier type and density in Mn(Bi,Sb)4Te7 Yingdong Guan, Seng Huat Lee, Zhiqiang Mao Intrinsic antiferromagnetic (AFM) topological insulators MnBi2nTe3n+1 (n=1, 2, 3) have attracted intense interest since they can support a variety of topological quantum states. The n=2 member, MnBi4Te7 was recently predicted to be a Weyl semimetal in its ferromagnetic phase [1,2]. To observe this state, tuning its magnetism from an AFM to ferromagnetic (FM) state is necessary and its chemical potential m is also required to be tuned to the charge neutrality point (CNP). In this talk, we will show these desired features are accessible in the Mn(Bi1-xSbx)4Te7 alloy system. We find both the charge carrier type and concentration can be systematically tuned by the Sb concentration, with m being close to the CNP at x ~ 0.27. Our established phase diagram also shows the FM phase is accessible in a wide range of x, but is suppressed when the carrier density is low, implying the interlayer FM coupling is mediated by the RKKY interaction. Furthermore, we also observed strong quantum oscillations in the samples with low carrier density, from which evidence of Fermi surface reconstruction caused by the FM transition is also observed. This result, together with the negative longitudinal magnetoresistance, suggests a possible FM Weyl state in Mn(Bi1-xSbx)4Te7 with x~0.27. |
Thursday, March 9, 2023 9:36AM - 9:48AM |
S43.00007: Hydrogen-tuned magnetotransport anisotropy and bandstructure of MnSb2Te4 Entela Buzi, Xiaxin Ding, Afrin Nahar Tamanna, Ayesha Lakra, Haiming Deng, Kamil Sobczak, Kyungwha Park, Lia Krusin-Elbaum In low dimensional systems magnetic anisotropy is at the root of long-range magnetic order and is vital in spintronic applications, most strikingly when the nontrivial topology of electronic bands is at play. Recent focus has been on the layered low-disorder antiferromagnet (AFM) MnBi2Te4 (MBT), shown to host topological surface Dirac bands supporting quantum anomalous Hall (QAH) and axion insulator states. Both, the band topology and magnetic anisotropy can be strongly affected by magnetic disorder, and current debate has centered around the topological nature of the isostructural to MBT yet a largely antisite-disordered MnSb2Te4 (MST). Depending on the level of Mn disorder, MST can be grown as an AFM or a ferromagnet (FM). Here we report on the post-growth tuning of magnetic anisotropy and the bandstructure of MST by injecting/extracting ionic hydrogen (H+). Our magnetotransport studies of MST under different field orientations reveal that hydrogenation tilts the spin direction from the out-of-plane (H||c) towards in-plane (H||ab), inducing a noncollinear spin structure that leads to transforming the initially an FM MST to canted AFM. Removal of H+ reverts MST to an FM state featuring topological chiral channels. This transition, investigated by DFT calculations, is due to hydrogen weakly binding to Mn. The role of hydrogen-healed Mn-Te dangling bonds will be discussed. |
Thursday, March 9, 2023 9:48AM - 10:00AM |
S43.00008: Pressure tuning of electronic and magnetic properties in a topological antiferromagnet Su Kong Chong, David E Graf, Chao Lei, Seng Huat Lee, Masaki Tanabe, Ting-Hsun Yang, Zhiqiang Mao, Allan H MacDonald, Kang-Lung Wang The antiferromagnetic interlayer exchange coupling in MnBi2Te4-based magnetic topological insulators gives rise to rich magnetic states as distinguished by their spin configurations. Reversible control of the magnetism and band topology is greatly sought after to access their unexplored quantum states and achieve better control of these states. Mechanical modulations of the lattice structure serve as an effective tuning parameter, which can manipulate the electronic band structures and modify the crystal field splitting, leading to the interplay of magnetic and topological phases. Here, we studied the magnetotransport properties of the MnBi2Te4 thin films under hydrostatic pressure. We observed a reversible control of both the magnetic and topological phases by high pressure at different magnetic fields. Our results suggest that pressure allows a tuning of the surface exchange interaction and the Chern insulator state. |
Thursday, March 9, 2023 10:00AM - 10:12AM |
S43.00009: Tunable magnetic domains in ferrimagnetic MnSb2Te4 Tatiana A Webb, Xiaxin Ding, Afrin Nahar Tamanna, Cory R Dean, Dmitri N Basov, Lia Krusin-Elbaum, Abhay N Pasupathy Highly tunable properties make the Mn(Bi,Sb)2Te4 phase diagram a rich playground for exploring the interplay between band topology and magnetism: On one end, MnBi2Te4 (MBT) hosts axion insulator and Chern insulating states [1,2], while the band topology of Sb-substituted MnSb2Te4 (MST) is potentially sensitive to defect disorder [3]. In this work, we use magnetic force microscopy (MFM) to characterize the ferrimagnetic domains of MST. We find that an external magnetic field can be used to tune between distinct stripe and bubble domain morphologies. Moreover, the low coercive field makes it possible to manipulate domains with the MFM tip. With in-situ transport, we quantify the impact of individual domains on device properties. This work opens the door to writable domain-based devices in the M(B,S)T family. |
Thursday, March 9, 2023 10:12AM - 10:24AM |
S43.00010: Metastability and topology in the magnetic topological insulator MnBi2Te4 Jeonghwan Ahn, Ganesh Panchapakesan, Jaron T Krogel MnBi2Te4 (MBT) has generated great interest as a first possible realization of an intrinsic topological insulator with A-type antiferromagnetic order. However, consistent observation of the surface gap formation with synthesized MBT samples has remained a challenge. Motivated by the observation of stacking faults, we have explored the possible existence of metastable local stacking modes at the MBT surface and their influence on the topological surface states. To this end, we used PBE+U calculations where Hubbard U was tuned with diffusion Monte Carlo techniques. We find that spin-orbit and van der Waals interactions are intertwined, which stabilizes the experimentally observed interlayer distance, and stacking. This stabilization can be understood in terms of interlayer hybridization among pz orbitals of Bi and Te. We further demonstrate that deviation from this optimal interlayer distance leads to a topological phase transition from a non-trivial to a trivial topology. The topological properties of a metastable stacking mode at the MBT surface, which directly induces a larger interlayer separation, will also be discussed. |
Thursday, March 9, 2023 10:24AM - 10:36AM |
S43.00011: Optical Kerr effect and Terahertz spectroscopy in an intrinsic ferromagnetic topological insulator Xingyue Han, Hee Taek Yi, Seongshik Oh, Liang Wu Incorporating magnetism into topology has brought exotic properties due to time-reversal symmetry breaking. In the case of magnetic topological insulators, the exchange gap emerges at the surface and induces quantum anomalous Hall effect (QAHE). The antiferromagnetic material MnBi2Te4 is the first intrinsic magnetic TI confirmed by experiments. However, the van der Waals compound shows a distinct dependence on the even-odd layers and the QAHE is only realized in the uncompensated odd layers. It remains elusive about an intrinsic ferromagnetic TI. In this work, we report a newly discovered ferromagnetic topological insulator, Cr(Bi,Sb)6Te10 (CBST). The large magneto-optical Kerr effect determines the ferromagnetic order and a high Curie temperature. It also shows a large terahertz Faraday and Kerr rotation that preserve below the transition temperature. Our work shows that CBST is a good platform to search for QAHE at high temperature. |
Thursday, March 9, 2023 10:36AM - 10:48AM |
S43.00012: Delicate Ferromagnetism in MnBi6Te10 Shuolong Yang, Chenhui Yan, Yanglin Zhu, Leixin Miao, Sebastian Fernandez-Mulligan, Emanuel Green, Ruobing Mei, Hengxin Tan, Binghai Yan, Chaoxing Liu, Nasim Alem, Zhiqiang Mao Tailoring magnetic orders in topological insulators is critical to the realization of topological quantum phenomena. An outstanding challenge is to find a material where atomic defects lead to tunable magnetic orders while maintaining a nontrivial topology. Here, by combining magnetization measurements, angle-resolved photoemission spectroscopy, and transmission electron microscopy, we reveal disorder-enabled, tunable magnetic ground states in MnBi6Te10. In the ferromagnetic phase, an energy gap of 15 meV is resolved at the Dirac point on the MnBi2Te4 termination. In contrast, antiferromagnetic MnBi6Te10 exhibits gapless topological surface states on all terminations. Transmission electron microscopy and magnetization measurements reveal substantial Mn vacancies and Mn migration in ferromagnetic MnBi6Te10. We provide a conceptual framework where a cooperative interplay of these defects drives a delicate change of overall magnetic ground state energies, and leads to tunable magnetic topological orders. Our work provides a clear pathway for nanoscale defect-engineering towards the realization of topological quantum phases. |
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