Bulletin of the American Physical Society
APS March Meeting 2024
Monday–Friday, March 4–8, 2024; Minneapolis & Virtual
Session T17: Experimental Advances in Topological Materials |
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Sponsoring Units: DCMP Chair: Md. Shafayat Hossain, Princeton University Room: M100H |
Thursday, March 7, 2024 11:30AM - 11:42AM |
T17.00001: Evidence for quantum spin Hall effect in a new van der Waals monolayer Jian Tang, Siyuan Ding, Hongyu Chen, Anyuan Gao, Tiema Qian, Zumeng Huang, Zhe Sun, Kenji Watanabe, Takashi Taniguchi, David C Bell, Ziqiang Wang, Liang Fu, Yang Zhang, Xiaofeng Qian, Kenneth S Burch, Youguo Shi, Ni Ni, Guoqing Chang, Su-Yang Xu, Qiong Ma Inspired by fundamental and technological interest, extensive efforts have been devoted to predicting and identifying high-quality quantum spin Hall (QSH) insulators. The van der Waals (vdW) monolayer TaIrTe4 has been predicted to be a large-gap QSH insulator by first-principles calculations. However, experimental evidence has been so far lacking. Leveraging refined vdW device fabrication techniques, we access the intrinsic quantum electronic properties of monolayer TaIrTe4. In this talk, we report experimental evidence pointing to the QSH effect in the TaIrTe4 monolayer. |
Thursday, March 7, 2024 11:42AM - 11:54AM |
T17.00002: Evidence for correlated states in a topological van der Waals monolayer. Siyuan Ding, Jian Tang, Hongyu Chen, Kenji Watanabe, Takashi Taniguchi, Ziqiang Wang, Liang Fu, Yang Zhang, Xiaofeng Qian, Kenneth S Burch, Youguo Shi, Ni Ni, Guoqing Chang, Suyang Xu, Qiong Ma Introducing electron correlations to topological materials can lead to the emergence of new quantum states of matter. We found that natural topological van der Waals (vdW) crystals MM′X4 (M = Nb, Ta and M′ = Ir, Rh) could be an exciting new platform to study the interplay of correlation and topology. In this talk, we report experimental evidence as well as tentative theoretical understanding of correlated states in a monolayer MM′X4. |
Thursday, March 7, 2024 11:54AM - 12:06PM |
T17.00003: Exchange Biased Anomalous Hall Effect in Chern Insulators Bo Chen, Xiaoda Liu, Yuhang Li, Han Tay, Takashi Taniguchi, Kenji Watanabe, Moses H Chan, Jiaqiang Yan, Fengqi Song, Ran Cheng, Cui-Zu Chang A central theme in condensed matter physics is the interplay between magnetism and topology, which gives rise to many exciting quantum phenomena, including the quantum anomalous Hall (QAH) state and axion insulator state. Over the past five years, the intrinsic antiferromagnetic (AFM) topological insulator (TI) MnBi2Te4 has attracted much attention, primarily due to the realization of the QAH and axion insulator states in odd and even number layers, respectively. However, the existence of native defects in MnBi2Te4, such as Mn/Bi antisites and Te vacancies, has greatly hindered the realization of these two phenomena. In this work, based on the manually exfoliated MnBi2Te4 thin flakes, we fabricated a series of MnBi2Te4 devices with the thickness of 5 septuple layers (SLs) to 8SLs. We first demonstrated the presence of the Chern insulator state under high magnetic field (> 6T). We observed a large negative exchange bias effect in odd-number layer devices, while this effect is absent in the even-layer samples. Our theoretical calculations suggest that the layer-dependent exchange biased anomalous Hall effect is a result of the formation of the surface reconstruction in MnBi2Te4, particularly near zero magnetic field. |
Thursday, March 7, 2024 12:06PM - 12:18PM |
T17.00004: Engineering Plateau Phase Transition via Tailoring Structure in Quantum Anomalous Hall Multilayers Deyi Zhuo, Ling-Jie Zhou, Yi-Fan Zhao, Ruoxi Zhang, Zi-Jie Yan, Annie G Wang, Moses H Chan, Chao-Xing Liu, Cui-Zu Chang The plateau phase transition in quantum anomalous Hall (QAH) insulators corresponds to a quantum state wherein a single magnetic domain gives way to multiple magnetic domains and then re-converges back to a single magnetic domain. The layer structure has been established as an external knob for adjusting the Chern number C of the QAH insulators. In this work, we employed molecular beam epitaxy (MBE) to grow magnetic TI multilayers with an asymmetric layer structure and realize the magnetic field-driven plateau phase transition between two QAH states with odd Chern number change DC. In a single multilayer structure with C = ±1 and C = ±2 QAH states, we found two characteristic power-law behaviors between temperature and the scaling variables on the magnetic field at the transition points. We extracted two critical exponents κ1 ~0.390 and κ2 ~0.388 for the plateau phase transitions with DC = 1 and DC = 3 in QAH insulators, respectively. This work will motivate further investigations into the critical behaviors of plateau phase transitions with different DC in QAH insulators and provide new opportunities for the development of QAH chiral edge current-based electronic and spintronic devices. |
Thursday, March 7, 2024 12:18PM - 12:30PM |
T17.00005: Study of the Impact of Ionic Liquid Gating and Uniaxial Strain on the Strongly Correlated Electron Material Samarium Hexaboride (SmB6) Dmitri Mihaliov, Shriya Sinha, Eric Chandler, Alexa I Rakoski, Priscila Rosa, Cagliyan Kurdak Samarium Hexaboride (SmB6) is a strongly correlated electron material well known for its robust insulating bulk and its topologically protected surface states. In this study, we analyze the influence of electrostatic doping through ionic liquid gating and applied pressure via uniaxial strain on the electrical resistance behavior of SmB6. Magneto-transport studies on SmB6 are complicated by conductive subsurface cracks, which strongly pollute Hall measurements. To minimize the effects, Hall bar samples were prepared by polishing all four elongated surfaces. Furthermore, data analysis was carried out by converting to Hall conductivity from resistivity due to a lessened effect of subsurface cracks. The small size of the samples meant that the scale of the contacts could not be treated as negligibly small. Thus, to accurately obtain the bulk and surface transport parameters, we performed finite element analysis on our geometries. Ionic liquid was used to modify the charge carrier density on the surface between applied voltages of -2 and 2 V. Within this range the resistance plateau varied as much as 75%. Using a strain cell, we measured a Hall bar under compression and tension, and we found variations in the resistance plateaus that were notably less pronounced compared to previous literature. |
Thursday, March 7, 2024 12:30PM - 12:42PM |
T17.00006: Disentangling surface conducting and bulk insulating behaviour in a d-electron topological insulator Nicholas Popiel, Alexander G Eaton, Ke-Jun Xu, Alexander J Hickey, Hsu Liu, Monica Ciomaga Hatnean, Geetha Balakrishnan, Gunnar F Lange, Robert-Jan Slager, Zhixun Shen, Suchitra Sebastian Transport measurements in f-electron insulators have revealed a new class of materials with conducting surface states of potential topological character. Strong electron-electron interactions in these materials allow for 2D electron physics to be explored in a bulk system. An open question remains as to whether these conducting surface states can exist in the absence of heavy f-electron physics. Experimental results are presented for transport measurements on a d-electron topological insulator candidate. Signatures of a conducting surface state are found for temperatures ⪅ 5 K and seen to vanish at higher temperatures. A new paradigm in which conducting surface states emerge due to strong electron-electron interactions and potential topological effects in d-electron systems is discussed. |
Thursday, March 7, 2024 12:42PM - 12:54PM |
T17.00007: Surface magnetotransport of FeSb2 single crystals Jarryd Horn, Yun Suk Eo, Hyeok Yoon, Johnpierre Paglione, Ryan Dorman Extensive study of over a dozen f-electron based Topological Kondo Insulator (TKI) candidate materials, such as SmB6 and Ce3Bi4Pt3, have led to a deep understanding of the role localized f-electrons play in the formation of a robust bulk correlated energy gap along with topologically protected surface conduction states in these materials. Recently, however, the observation of surface states and Kondo-like behavior in some d-electron materials is beginning to motivate further research to expand the understanding of TKIs into a new class of potential TKIs which include FeSi and FeSb2. Using the inverted resistance method of separating bulk and surface contributions to electronic transport, our recent results have unambiguously demonstrated direct evidence of metallic surface conduction in FeSb2 at low temperatures, revealing 2D metallic behavior on the surface of an extraordinarily robust insulating bulk single crystal. We have expanded this effort to probe the magnetic field dependence and symmetry of the surface conduction states in FeSb2 while investigating the contributions to the transport behavior from intrinsic crystalline anisotropy as well as extrinsic surface and bulk defects. |
Thursday, March 7, 2024 12:54PM - 1:06PM |
T17.00008: Preservation of Topological Surface States in Wafer-Scale Transferred Membranes Qiang Gao, Chi Ian Ip, Chenhui Yan, Khanh Duy Nguyen, Gangbin Yan, Eli Hoenig, Thomas Marchese, Minghao Zhang, Woojoo Lee, Hossein Rokni, Ying Shirley Meng, Chong Liu, Shuolong Yang Ultrathin topological insulator membranes have been proposed to be building blocks of exotic quantum matters. However, traditional epitaxial growth does not facilitate material stacking in arbitrary orders, while mechanical exfoliation from bulk topological insulator crystals is also challenging due to the non-negligible interlayer coupling therein. Here we liberate wafer-scale ultrathin films of topological insulator Bi2Se3, grown by molecular beam epitaxy, down to the thickness of 3 quintuple layers. We characterize the preservation of the topological surface states and quantum well states using angle-resolved photoemission spectroscopy. With this liberation method, we fabricate free-standing topological insulator membranes and reveal the local strain effect near the grain boundaries using scanning transmission electron microscopy. Our work delineates the essential material processing protocol to explore the fundamental properties and applications in topological insulator thin films and heterostructures. |
Thursday, March 7, 2024 1:06PM - 1:18PM |
T17.00009: Crystal defect control of topological insulator Bi2Se3 using a new modified Bridgman crystal growth method Yingdong Guan, Suguru Yoshida, Zhiqiang Mao Bridgman growth, which is a prevalent method for melt-based single crystal growth, often has limited control on crystal defects. For instance, topological insulator Bi2Se3 grown using conventional Bridgman method is often heavily doped due to the high-density crystal defects caused by nonstoichiometric composition. In this talk, we will introduce a new modified Bridgman method, i.e. double crucible vertical Bridgman (DCVB), which has potential to grow crystals with precisely controlled chemical composition. This method uses a double-crucible geometry with the upper crucible continuously feeding source material to the bottom growth crucible. Moreover, this system also allows for applying high pressure (up to 10 atm) and implementing chemical encapsulation. The combination of these advantages enables the control of composition of the melt in the growth crucible, thus improving the quality of grown crystals. We took Bi2Se3 as an example to demonstrate DCVB growth. Our preliminary test growths have shown that the carrier density of DCVB-grown Bi2Se3 single crystal is as low as ~ 8.5*1017, which is already one or two orders of magnitude smaller than those crystals grown using conventional melt/Bridgman growth methods, indicating that DCVB growth can lower crystal defect density. |
Thursday, March 7, 2024 1:18PM - 1:30PM |
T17.00010: Magnetotransport studies on topological insulator candidate: 1T'-WSe2 Yangchen He, Nicholas Pederson, Kenji Watanabe, Takashi Taniguchi, Shermane M Benjamin, Luis Balicas, Daniel Rhodes The family of 1T’-MX2 (M = W, Mo, and X = Te, Se, S) have been predicted to be Quantum Spin Hall Insulators (QSHI), hosting edge states that could realize dissipationless current transport at high temperatures. However, beyond WTe2, there has been no experimental verification of the spin-polarized edge states in the 1T’-MX2 family. Recent scanning tunneling microscopy (STM) and angle-resolved photoemission spectroscopy (ARPES) studies have suggested that monolayer 1T’-WSe2 grown by molecular beam epitaxy hosts conductive edge states with a concomitant large bulk band gap (~129 meV). Here, we report on the synthesis of high quality 2M-WSe2 single crystals (the bulk stacking order of 1T’-WSe2 monolayer) and studies of the Fermiology. In addition, we will discuss the magnetotransport behavior and gate-tunability of few-layer devices. |
Thursday, March 7, 2024 1:30PM - 1:42PM |
T17.00011: Top-down patterning of topological surface and edge states using a focused ion beam Julie Karel, Qi Zhang, Abuduliken Bake, Zengji Yue, Xiaolin Wang, Grace Causer, Roger Lewis, Golrokh Akhgar, Mitchell Nancarrow, Alexander Nguyen, Zeljko Pastuovic, Weiyao Zhao, Jared Cole, Cong Son Ho, Nagarajan Valanoor, David Cortie Conducting boundary states in a topological insulator offer enormous potential in low energy quantum electronics. Key to efforts to develop topological electronics is the ability to precisely control the location of these states in materials. This talk will show spatial patterning of metallic edge and surface states in a single crystal of the well-known topological insulator, Sb2Te3. A focused ion beam, with appropriate fluence, can be used to drive a structural phase transition from a single crystal to an amorphous structure. It will be shown that this structural transition results in a concomitant topological phase transition from ℤ2s=1 → ℤ2s=0. The amorphous structure presents trivial, insulating bulk and surface states. Finally, experimental results will be compared with density function theory calculations, and prospects for future applications will be discussed. |
Thursday, March 7, 2024 1:42PM - 1:54PM |
T17.00012: Spherical Polarization Analysis for Measuring Spin Hall Materials Guga Khundzakishvili, Jacob Tosado, Peter Jiang, Barry Winn, Gavin L Hester, Colten Koogler, Robert Cooper, Neel Jain, Kevin Goodman, Wei Xie, Yong P Chen, Arnab Banerjee Topological Insulators (TI) combine charge order and spin-orbit coupling leading to an insulating bulk, yet topological surface conduction states. Here we present the results of polarized neutron scattering experiment(s) on single crystal of Bi2Se3, showing a cross-interaction of the polarized surface conduction states with the incident neutron beam polarization. This is significant as it could open possibilities of Topological Insulators being used as polarized neutron detectors and allow a novel probe for TI surface states. |
Thursday, March 7, 2024 1:54PM - 2:06PM |
T17.00013: Interfacial thermal resistance in topological phases Min Young Kim, Minyue Zhu, Joon Sang Kang, Joseph P Heremans Bi1-xSbx alloys have various band structures depending on the Sb concentration.1 In particular, when x is above 10%, the Bi1-xSbx alloys can be in topological insulator (TI) phase with the inverted band ordering of L bands, and the band gap can get reopened as temperature rises because lattice constant changes.2,3 In this work, we use the band gap opening of TI Bi1-xSbx alloys with the increase of temperature and the accompanying phase transition from topological insulator into trivial semiconductor to study the thermal properties of the topological interface states near the Fermi level. By measuring the frequency-domain thermoreflectance (FDTR) data on Au/Bi0.93Sb0.07, Bi0.9Sb0.1 and Bi0.87Sb0.13, we discover an abrupt change in interfacial thermal conductance of Au/Bi1-xSbx system that occurs at the TI/trivial transition point. We attribute it to the change of thermal transport of electrons at the surface of Bi1-xSbx. This discovery might lead to the development of a proof-of-concept for all-solid-state thermal switches and regulators. |
Thursday, March 7, 2024 2:06PM - 2:18PM |
T17.00014: Edge Mode Transport through Nanoscale Channels in the Topological Insulator Cadmium Arsenide Simon Munyan, Binghao Guo, William Huynh, Victor Huang, Susanne Stemmer Two-dimensional topological insulators (2D TIs) can feature dissipationless, one-dimensional charge transport via edge modes, offering a rich ground for studying exotic quasi-particles and geometric phases useful for quantum information applications. However, there are few experimentally-realized 2D TIs with clear edge mode transport, and their coherence is typically limited by disorder to short length scales. In this work, we study the edge mode transport of the 2D TI Cd3As2 in nanoscale channels defined by finger gates. At finite magnetic field, we demonstrate selective transmission of quantum Hall edge modes through the channel by tuning the finger gate. We find that localized states arising from disorder facilitate percolation of reflected edge modes through the channel when the finger gate is tuned through a Landau level. We study the device in the unipolar and bipolar regimes and confirm non-spin-selective equilibration between edge modes, which is unique to systems with strong spin-orbit coupling. In accordance with past work on quantum point contacts in Cd3As2, we observe a remnant conductance when the channel is tuned into the topological gap, suggesting conduction via helical edge modes through the channel. Exact quantization is precluded by broken time reversal symmetry and disorder, which we address with experiments at zero field and by varying the channel width. |
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