Zijie Yan

All Publications

• Designing Magnetic Topological Insulator Trilayers for Highly Efficient Spin-Orbit Torque Switching NANO LETTERS Zhou, L., Zhuo, D., Tay, H., Yan, Z., Xiao, P., Liu, X., Zhang, B., Chang, C. 2026; 26 (23): 7833-7840

  Abstract

  Spin-orbit torque (SOT) enables efficient electrical control of magnetization, offering a pathway toward low-power spintronic devices. Magnetic topological insulators (TIs), with spin-momentum-locked surface states and intrinsic ferromagnetism, provide a unique platform for switching the edge-current chirality in quantum anomalous Hall (QAH) insulators. Here, we employ molecular beam epitaxy to synthesize a series of magnetic TI trilayers with controlled layer thicknesses on heat-treated SrTiO3(111) substrates. Electrical transport measurements reveal that SOT-driven magnetization reversal and the associated switching of QAH edge current chirality are governed by a SrTiO3(111) substrate-induced charging effect, which generates a chemical potential asymmetry between the top and bottom magnetic TI layers. The switching polarity and efficiency are further tuned through heterostructure design, gate voltage, and an in-plane magnetic field. These findings identify chemical-potential asymmetry as the key mechanism for achieving a large SOT switching ratio and establish a route toward electrical control of edge current and QAH-based logic and memory devices.

  View details for DOI 10.1021/acs.nanolett.6c02154

  View details for Web of Science ID 001784767000001

  View details for PubMedID 42237482

  View details for PubMedCentralID PMC13281699

• Orbital-hybridization-induced Ising-type superconductivity in a confined gallium layer NATURE MATERIALS Yi, H., Liu, Y., Dong, C., Yang, Y., Yan, Z., Wang, Z., Zhou, L., Wu, D., Chen, H., Paolini, S., Xia, B., Zhang, B., Liu, X., Rong, H., Wang, A. G., Mandal, S., Yang, K., Katz, B. N., Hu, L., Liu, J., Lee, T., Crespi, V. H., Wang, Y., Chen, Y., Robinson, J. A., Liu, C., Chang, C. 2026; 25 (7): 1175-1181

  Abstract

  In low-dimensional superconductors, the interplay between quantum confinement and interfacial hybridization effects can reshape Cooper-pair wavefunctions and give rise to unconventional superconducting states. Here we use plasma-free confinement epitaxy assisted by a carbon buffer layer to synthesize a gallium trilayer sandwiched between graphene and a 6H-SiC(0001) substrate. Within this confined gallium layer, we demonstrate interfacial Ising-type superconductivity driven by atomic orbital hybridization. Electrical transport measurements reveal that the in-plane upper critical magnetic field reaches ~21.98 T at T = 400 mK, approximately 3.38 times the Pauli paramagnetic limit. Angle-resolved photoemission spectroscopy measurements, combined with theoretical calculations, confirm the presence of split Fermi surfaces with Ising-type spin textures at the K and K' valleys of the confined gallium layer, originating from strong hybridization with the SiC substrate. This work establishes a strategy for realizing unconventional pairing wavefunctions through the synergistic combination of quantum confinement and interfacial hybridization effects.

  View details for DOI 10.1038/s41563-026-02573-y

  View details for Web of Science ID 001739702400001

  View details for PubMedID 41975080

  View details for PubMedCentralID 7935850

• Moiré engineering of Cooper-pair density modulation states NATURE Wang, Z., Xia, B., Paolini, S., Yan, Z., Xiao, P., Song, J., Gowda, V., Rong, H., Xiao, D., Xu, X., Wu, W., Wang, Z., Chang, C. 2026; 652 (8109): 335-341

  Abstract

  Cooper-pair density modulation (CPDM) states are superconducting phases in which the order parameter varies periodically in real space without breaking translational symmetry1-3. Moiré superlattices in layered materials4-18 have recently emerged as powerful platforms for engineering charge density with tunable lattice symmetry, offering a new route to creating and controlling CPDM states. Here we demonstrate moiré-induced CPDM states in a bilayer heterostructure formed by epitaxially stacking one quintuple layer (1QL) of topological insulator Sb2Te3 on a six-unit-cell (6UC) antiferromagnetic FeTe layer. Scanning tunnelling microscopy and spectroscopy (STM/S) measurements reveal a moiré superlattice formed between the hexagonal tellurium lattice of Sb2Te3 and the square tellurium lattice of FeTe, which spatially modulates the two superconducting gaps of the 1QL Sb2Te3/6UC FeTe bilayer. Our Josephson STM/S measurements provide direct real-space imaging of the CPDM states with a wavelength corresponding to the periodicity of the moiré superlattice. By substituting Sb2Te3 with Bi2Te3, we achieve control over both the periodicity and magnitude of the CPDM states. Our work demonstrates an epitaxial strategy for synthesizing moiré superlattices from materials with different crystal symmetries and reveals a new mechanism for engineering CPDM states in designer bilayer heterostructures.

  View details for DOI 10.1038/s41586-026-10325-w

  View details for Web of Science ID 001730632800001

  View details for PubMedID 41922761

  View details for PubMedCentralID 10307636

• Stoichiometric FeTe is a superconductor NATURE Yan, Z., Wang, Z., Xia, B., Paolini, S., Chan, Y., Dihingia, N., Rong, H., Xiao, P., Halanayake, K. D., Song, J., Gowda, V., Hickey, D., Wu, W., Yu, J., Hirschfeld, P. J., Chang, C. 2026; 652 (8109): 342-348

  Abstract

  Iron-based superconductors (FeSCs) are a fascinating family of materials in which several electronic bands and strong antiferromagnetic (AFM) correlations are key ingredients for competing ground states1-6, including antiferromagnetism, electronic nematicity and unconventional superconductivity. FeTe, unlike its superconducting isostructural counterpart FeSe, has long been considered an AFM metal sans superconductivity7-9. Here we use molecular-beam epitaxy (MBE) to grow FeTe films and perform post-growth annealing under a Te flux. By performing spin-polarized scanning tunnelling microscopy and spectroscopy (STM/S), we demonstrate that the AFM order in as-grown FeTe films is induced by interstitial Fe atoms that disrupt the ideal 1:1 stoichiometry. Notably, the removal of these interstitial Fe atoms through Te annealing yields stoichiometric FeTe films that show no AFM order and instead exhibit robust superconductivity with a critical temperature of about 13.5 K. This superconducting state is further confirmed by the observation of Cooper-pair tunnelling, zero electrical resistance and the Meissner effect. Therefore, our results demonstrate that stoichiometric FeTe is inherently a superconductor, overturning a long-held view that it is an AFM metal. This work clarifies the origin of superconductivity in FeTe-based heterostructures10-15 and demonstrates the importance of stoichiometry control in understanding the competition between antiferromagnetism and superconductivity in FeSCs.

  View details for DOI 10.1038/s41586-026-10321-0

  View details for Web of Science ID 001730622600001

  View details for PubMedID 41922766

  View details for PubMedCentralID 10628154

• Interplay of Quantum Size Effect and Tensile Strain on Surface Morphology of β-Sn(100) Islands ACS NANO Xia, B., Li, X., Chen, H., Yang, B., Cai, J., Paolini, S., Wang, Z., Yan, Z., Yang, H., Liu, X., Liu, L., Guan, D., Wang, S., Li, Y., Liu, C., Zheng, H., Chang, C., Liu, F., Jia, J. 2026; 20 (10): 8289-8297

  Abstract

  The quantum size effect (QSE) and strain effect are two key factors influencing the surface morphology of thin films, which can increase film surface roughness through QSE-induced thickness oscillation and strain-induced island formation, respectively. Surface roughness usually manifests in the early stages of film growth and diminishes beyond a critical thickness. In this work, we employ molecular beam epitaxy (MBE) to grow β-Sn(100) islands with varying thickness N on bilayer graphene-terminated 6H-SiC(0001) substrates. Scanning tunneling microscopy and spectroscopy measurements reveal an inverse surface roughness effect that highlights the interplay of QSE and misfit strain in shaping the surface morphology of β-Sn(100) islands. For N ≤ 10, the islands exhibit flat surfaces, while for N ≥ 26, the island surfaces become corrugated and patterned. For the intermediate range, i.e., 12 ≤ N ≤ 24, both flat and patterned surfaces coexist, with the percentage coverage of the patterned surface oscillating as a function of N. By performing density functional theory calculations, we demonstrate that the unusual surface pattern evolution in our MBE-grown β-Sn(100) islands is a result of the interplay between QSE-induced surface roughing and tensile strain-induced smoothening effect.

  View details for DOI 10.1021/acsnano.5c14019

  View details for Web of Science ID 001705605100001

  View details for PubMedID 41771291

  View details for PubMedCentralID PMC13001075

• Meissner Effect and Nonreciprocal Charge Transport in Non-Topological 1T-CrTe2/FeTe Heterostructures ADVANCED MATERIALS Yan, Z., Chan, Y., Yuan, W., Wang, A. G., Yi, H., Wang, Z., Zhou, L., Rong, H., Zhuo, D., Wang, K., Singleton, J., Winter, L. E., Wu, W., Chang, C. 2026; 38 (14): e20598

  Abstract

  Interface-induced superconductivity has recently been achieved by stacking a magnetic topological insulator layer on an antiferromagnetic FeTe layer. However, the mechanism driving this emergent superconductivity remains unclear. Here, we employ molecular beam epitaxy to grow a 1T-CrTe2 layer, a 2D ferromagnet with a Curie temperature up to room temperature, on a FeTe layer. These 1T-CrTe2/FeTe heterostructures show superconductivity with a critical temperature of ∼12 K. Through magnetic force microscopy measurements, we observe the Meissner effect on the surface of the 1T-CrTe2 layer. Our electrical transport measurements reveal that the 1T-CrTe2/FeTe heterostructures exhibit nonreciprocal charge transport behavior, characterized by a large magneto-chiral anisotropy coefficient. The enhanced nonreciprocal charge transport in 1T-CrTe2/FeTe heterostructures provides a promising platform for exploring the magnetically controllable superconducting diode effect.

  View details for DOI 10.1002/adma.202520598

  View details for Web of Science ID 001680379800001

  View details for PubMedID 41641869

  View details for PubMedCentralID PMC12966969

• Depth-resolved magnetic order in superconducting topological insulator/FeTe thin film heterostructures PHYSICAL REVIEW MATERIALS Balakrishnan, P. P., Yi, H., Yan, Z., Yuan, W., Suter, A., Jensen, C. J., Manuel, P., Orlandi, F., Hanashima, T., Kinane, C. J., Caruana, A. J., Backes, D., Shafer, P., Maranville, B. B., Salman, Z., Prokscha, T., Chang, C., Grutter, A. J. 2025; 9 (10)

  View details for DOI 10.1103/15fx-3cr2

  View details for Web of Science ID 001613242600002

• Interlayer exchange coupling induced critical-metal-to-insulator phase transition in quantum anomalous Hall insulators PHYSICAL REVIEW B Zhang, R., Zhao, Y., Zhou, L., Zhuo, D., Yan, Z., Liu, C., Chan, M. H. W., Chen, C., Chang, C. 2025; 112 (12)

  View details for DOI 10.1103/6myc-8pr9

  View details for Web of Science ID 001564197900013

• Interlayer coupling induced quantum phase transition in quantum anomalous Hall multilayers PHYSICAL REVIEW B Zhou, L., Zhuo, D., Mei, R., Zhao, Y., Yang, K., Zhang, R., Yan, Z., Tay, H., Chan, M. H. W., Liu, C., Chang, C. 2025; 111 (20)

  View details for DOI 10.1103/PhysRevB.111.L201304

  View details for Web of Science ID 001495127700002

• Coexistence of Superconductivity and Antiferromagnetism in Topological Magnet MnBi₂Te₄ Films NANO LETTERS Yuan, W., Yan, Z., Yi, H., Wang, Z., Paolini, S., Zhao, Y., Zhou, L., Wang, A. G., Wang, K., Prokscha, T., Salman, Z., Suter, A., Balakrishnan, P. P., Grutter, A. J., Winter, L. E., Singleton, J., Chan, M. H. W., Chang, C. 2024; 24 (26): 7962-7971

  Abstract

  The interface of two materials can harbor unexpected emergent phenomena. One example is interface-induced superconductivity. In this work, we employ molecular beam epitaxy to grow a series of heterostructures formed by stacking together two nonsuperconducting antiferromagnetic materials, an intrinsic antiferromagnetic topological insulator MnBi2Te4 and an antiferromagnetic iron chalcogenide FeTe. Our electrical transport measurements reveal interface-induced superconductivity in these heterostructures. By performing scanning tunneling microscopy and spectroscopy measurements, we observe a proximity-induced superconducting gap on the top surface of the MnBi2Te4 layer, confirming the coexistence of superconductivity and antiferromagnetism in the MnBi2Te4 layer. Our findings will advance the fundamental inquiries into the topological superconducting phase in hybrid devices and provide a promising platform for the exploration of chiral Majorana physics in MnBi2Te4-based heterostructures.

  View details for DOI 10.1021/acs.nanolett.4c01407

  View details for Web of Science ID 001249662000001

  View details for PubMedID 38885199

• Engineering Plateau Phase Transition in Quantum Anomalous Hall Multilayers NANO LETTERS Zhuo, D., Zhou, L., Zhao, Y., Zhang, R., Yan, Z., Wang, A. G., Chan, M. H. W., Liu, C., Chen, C., Chang, C. 2024; 24 (23): 6974-6980

  Abstract

  The plateau phase transition in quantum anomalous Hall (QAH) insulators corresponds to a quantum state wherein a single magnetic domain gives way to multiple domains and then reconverges back to a single magnetic domain. The layer structure of the sample provides an external knob for adjusting the Chern number C of the QAH insulators. Here, we employ molecular beam epitaxy to grow magnetic topological insulator multilayers and realize the magnetic field-driven plateau phase transition between two QAH states with odd Chern number change ΔC. We find that critical exponents extracted for the plateau phase transitions with ΔC = 1 and ΔC = 3 in QAH insulators are nearly identical. We construct a four-layer Chalker-Coddington network model to understand the consistent critical exponents for the plateau phase transitions with ΔC = 1 and ΔC = 3. This work will motivate further investigations into the critical behaviors of plateau phase transitions with different ΔC in QAH insulators.

  View details for DOI 10.1021/acs.nanolett.4c01313

  View details for Web of Science ID 001238275500001

  View details for PubMedID 38829211

• Interface-induced superconductivity in magnetic topological insulators SCIENCE Yi, H., Zhao, Y., Chan, Y., Cai, J., Mei, R., Wu, X., Yan, Z., Zhou, L., Zhang, R., Wang, Z., Paolini, S., Xiao, R., Wang, K., Richardella, A. R., Singleton, J., Winter, L. E., Prokscha, T., Salman, Z., Suter, A., Balakrishnan, P. P., Grutter, A. J., Chan, M. H. W., Samarth, N., Xu, X., Wu, W., Liu, C., Chang, C. 2024; 383 (6683): 634-639

  Abstract

  The interface between two different materials can show unexpected quantum phenomena. In this study, we used molecular beam epitaxy to synthesize heterostructures formed by stacking together two magnetic materials, a ferromagnetic topological insulator (TI) and an antiferromagnetic iron chalcogenide (FeTe). We observed emergent interface-induced superconductivity in these heterostructures and demonstrated the co-occurrence of superconductivity, ferromagnetism, and topological band structure in the magnetic TI layer-the three essential ingredients of chiral topological superconductivity (TSC). The unusual coexistence of ferromagnetism and superconductivity is accompanied by a high upper critical magnetic field that exceeds the Pauli paramagnetic limit for conventional superconductors at low temperatures. These magnetic TI/FeTe heterostructures with robust superconductivity and atomically sharp interfaces provide an ideal wafer-scale platform for the exploration of chiral TSC and Majorana physics.

  View details for DOI 10.1126/science.adk1270

  View details for Web of Science ID 001183256400019

  View details for PubMedID 38330133

• Electrical switching of the edge current chirality in quantum anomalous Hall insulators NATURE MATERIALS Yuan, W., Zhou, L., Yang, K., Zhao, Y., Zhang, R., Yan, Z., Zhuo, D., Mei, R., Wang, Y., Yi, H., Chan, M. H. W., Kayyalha, M., Liu, C., Chang, C. 2024; 23 (1): 58-+

  Abstract

  A quantum anomalous Hall (QAH) insulator is a topological phase in which the interior is insulating but electrical current flows along the edges of the sample in either a clockwise or counterclockwise direction, as dictated by the spontaneous magnetization orientation. Such a chiral edge current eliminates any backscattering, giving rise to quantized Hall resistance and zero longitudinal resistance. Here we fabricate mesoscopic QAH sandwich Hall bar devices and succeed in switching the edge current chirality through thermally assisted spin-orbit torque (SOT). The well-quantized QAH states before and after SOT switching with opposite edge current chiralities are demonstrated through four- and three-terminal measurements. We show that the SOT responsible for magnetization switching can be generated by both surface and bulk carriers. Our results further our understanding of the interplay between magnetism and topological states and usher in an easy and instantaneous method to manipulate the QAH state.

  View details for DOI 10.1038/s41563-023-01694-y

  View details for Web of Science ID 001658094800001

  View details for PubMedID 37857889

• 3D Quantum Anomalous Hall Effect in Magnetic Topological Insulator Trilayers of Hundred-Nanometer Thickness ADVANCED MATERIALS Zhao, Y., Zhang, R., Sun, Z., Zhou, L., Zhuo, D., Yan, Z., Yi, H., Wang, K., Chan, M. H. W., Liu, C., Law, K. T., Chang, C. 2024; 36 (13): e2310249

  Abstract

  Magnetic topological states refer to a class of exotic phases in magnetic materials with the non-trivial topological property determined by magnetic spin configurations. An example of such states is the quantum anomalous Hall (QAH) state, which is a zero magnetic field manifestation of the quantum Hall effect. Current research in this direction focuses on QAH insulators with a thickness of less than 10 nm. Here, molecular beam epitaxy (MBE) is employed to synthesize magnetic TI trilayers with a thickness of up to ≈106 nm. It is found that these samples exhibit well-quantized Hall resistance and vanishing longitudinal resistance at zero magnetic field. By varying the magnetic dopants, gate voltages, temperature, and external magnetic fields, the properties of these thick QAH insulators are examined and the robustness of the 3D QAH effect is demonstrated. The realization of the well-quantized 3D QAH effect indicates that the nonchiral side surface states of the thick magnetic TI trilayers are gapped and thus do not affect the QAH quantization. The 3D QAH insulators of hundred-nanometer thickness provide a promising platform for the exploration of fundamental physics, including axion physics and image magnetic monopole, and the advancement of electronic and spintronic devices to circumvent Moore's law.

  View details for DOI 10.1002/adma.202310249

  View details for Web of Science ID 001135216500001

  View details for PubMedID 38118065

• Axion insulator state in hundred-nanometer-thick magnetic topological insulator sandwich heterostructures NATURE COMMUNICATIONS Zhuo, D., Yan, Z., Sun, Z., Zhou, L., Zhao, Y., Zhang, R., Mei, R., Yi, H., Wang, K., Chan, M. H. W., Liu, C., Law, K. T., Chang, C. 2023; 14 (1): 7596

  Abstract

  An axion insulator is a three-dimensional (3D) topological insulator (TI), in which the bulk maintains the time-reversal symmetry or inversion symmetry but the surface states are gapped by surface magnetization. The axion insulator state has been observed in molecular beam epitaxy (MBE)-grown magnetically doped TI sandwiches and exfoliated intrinsic magnetic TI MnBi2Te4 flakes with an even number layer. All these samples have a thickness of ~ 10 nm, near the 2D-to-3D boundary. The coupling between the top and bottom surface states in thin samples may hinder the observation of quantized topological magnetoelectric response. Here, we employ MBE to synthesize magnetic TI sandwich heterostructures and find that the axion insulator state persists in a 3D sample with a thickness of ~ 106 nm. Our transport results show that the axion insulator state starts to emerge when the thickness of the middle undoped TI layer is greater than ~ 3 nm. The 3D hundred-nanometer-thick axion insulator provides a promising platform for the exploration of the topological magnetoelectric effect and other emergent magnetic topological states, such as the high-order TI phase.

  View details for DOI 10.1038/s41467-023-43474-x

  View details for Web of Science ID 001116498500031

  View details for PubMedID 37989754

  View details for PubMedCentralID PMC10663498

• Dirac-fermion-assisted interfacial superconductivity in epitaxial topological-insulator/iron-chalcogenide heterostructures NATURE COMMUNICATIONS Yi, H., Hu, L., Zhao, Y., Zhou, L., Yan, Z., Zhang, R., Yuan, W., Wang, Z., Wang, K., Hickey, D., Richardella, A. R., Singleton, J., Winter, L. E., Wu, X., Chan, M. H. W., Samarth, N., Liu, C., Chang, C. 2023; 14 (1): 7119

  Abstract

  Over the last decade, the possibility of realizing topological superconductivity (TSC) has generated much excitement. TSC can be created in electronic systems where the topological and superconducting orders coexist, motivating the continued exploration of candidate material platforms to this end. Here, we use molecular beam epitaxy (MBE) to synthesize heterostructures that host emergent interfacial superconductivity when a non-superconducting antiferromagnet (FeTe) is interfaced with a topological insulator (TI) (Bi, Sb)2Te3. By performing in-vacuo angle-resolved photoemission spectroscopy (ARPES) and ex-situ electrical transport measurements, we find that the superconducting transition temperature and the upper critical magnetic field are suppressed when the chemical potential approaches the Dirac point. We provide evidence to show that the observed interfacial superconductivity and its chemical potential dependence is the result of the competition between the Ruderman-Kittel-Kasuya-Yosida-type ferromagnetic coupling mediated by Dirac surface states and antiferromagnetic exchange couplings that generate the bicollinear antiferromagnetic order in the FeTe layer.

  View details for DOI 10.1038/s41467-023-42902-2

  View details for Web of Science ID 001142811000028

  View details for PubMedID 37932274

  View details for PubMedCentralID PMC10628154

• Evolution of Dopant-Concentration-Induced Magnetic Exchange Interaction in Topological Insulator Thin Films NANO LETTERS Wang, F., Zhao, Y., Yan, Z., Zhuo, D., Yi, H., Yuan, W., Zhou, L., Zhao, W., Chan, M. H. W., Chang, C. 2023; 23 (7): 2483-2489

  Abstract

  To date, the quantum anomalous Hall effect has been realized in chromium (Cr)- and/or vanadium(V)-doped topological insulator (Bi,Sb)2Te3 thin films. In this work, we use molecular beam epitaxy to synthesize both V- and Cr-doped Bi2Te3 thin films with controlled dopant concentration. By performing magneto-transport measurements, we find that both systems show an unusual yet similar ferromagnetic response with respect to magnetic dopant concentration; specifically the Curie temperature does not increase monotonically but shows a local maximum at a critical dopant concentration. We attribute this unusual ferromagnetic response observed in Cr/V-doped Bi2Te3 thin films to the dopant-concentration-induced magnetic exchange interaction, which displays evolution from van Vleck-type ferromagnetism in a nontrivial magnetic topological insulator to Ruderman-Kittel-Kasuya-Yosida (RKKY)-type ferromagnetism in a trivial diluted magnetic semiconductor. Our work provides insights into the ferromagnetic properties of magnetically doped topological insulator thin films and facilitates the pursuit of high-temperature quantum anomalous Hall effect.

  View details for DOI 10.1021/acs.nanolett.2c03827

  View details for Web of Science ID 000962517500001

  View details for PubMedID 36930727

• Confinement-Induced Chiral Edge Channel Interaction in Quantum Anomalous Hall Insulators PHYSICAL REVIEW LETTERS Zhou, L., Mei, R., Zhao, Y., Zhang, R., Zhuo, D., Yan, Z., Yuan, W., Kayyalha, M., Chan, M. H. W., Liu, C., Chang, C. 2023; 130 (8): 086201

  Abstract

  In quantum anomalous Hall (QAH) insulators, the interior is insulating but electrons can travel with zero resistance along one-dimensional (1D) conducting paths known as chiral edge channels (CECs). These CECs have been predicted to be confined to the 1D edges and exponentially decay in the two-dimensional (2D) bulk. In this Letter, we present the results of a systematic study of QAH devices fashioned in a Hall bar geometry of different widths under gate voltages. At the charge neutral point, the QAH effect persists in a Hall bar device with a width of only ∼72  nm, implying the intrinsic decaying length of CECs is less than ∼36  nm. In the electron-doped regime, we find that the Hall resistance deviates quickly from the quantized value when the sample width is less than 1  μm. Our theoretical calculations suggest that the wave function of CEC first decays exponentially and then shows a long tail due to disorder-induced bulk states. Therefore, the deviation from the quantized Hall resistance in narrow QAH samples originates from the interaction between two opposite CECs mediated by disorder-induced bulk states in QAH insulators, consistent with our experimental observations.

  View details for DOI 10.1103/PhysRevLett.130.086201

  View details for Web of Science ID 000937275200005

  View details for PubMedID 36898119

• Proximity-induced superconductivity in epitaxial topological insulator/graphene/gallium heterostructures NATURE MATERIALS Li, C., Zhao, Y., Vera, A., Lesser, O., Yi, H., Kumari, S., Yan, Z., Dong, C., Bowen, T., Wang, K., Wang, H., Thompson, J. L., Watanabe, K., Taniguchi, T., Reifsnyder Hickey, D., Oreg, Y., Robinson, J. A., Chang, C., Zhu, J. 2023; 22 (5): 570-+

  Abstract

  The introduction of superconductivity to the Dirac surface states of a topological insulator leads to a topological superconductor, which may support topological quantum computing through Majorana zero modes1,2. The development of a scalable material platform is key to the realization of topological quantum computing3,4. Here we report on the growth and properties of high-quality (Bi,Sb)2Te3/graphene/gallium heterostructures. Our synthetic approach enables atomically sharp layers at both hetero-interfaces, which in turn promotes proximity-induced superconductivity that originates in the gallium film. A lithography-free, van der Waals tunnel junction is developed to perform transport tunnelling spectroscopy. We find a robust, proximity-induced superconducting gap formed in the Dirac surface states in 5-10 quintuple-layer (Bi,Sb)2Te3/graphene/gallium heterostructures. The presence of a single Abrikosov vortex, where the Majorana zero modes are expected to reside, manifests in discrete conductance changes. The present material platform opens up opportunities for understanding and harnessing the application potential of topological superconductivity.

  View details for DOI 10.1038/s41563-023-01478-4

  View details for Web of Science ID 000933171400002

  View details for PubMedID 36781950

• Creation of chiral interface channels for quantized transport in magnetic topological insulator multilayer heterostructures NATURE COMMUNICATIONS Zhao, Y., Zhang, R., Cai, J., Zhuo, D., Zhou, L., Yan, Z., Chan, M. H. W., Xu, X., Chang, C. 2023; 14 (1): 770

  Abstract

  One-dimensional chiral interface channels can be created at the boundary of two quantum anomalous Hall (QAH) insulators with different Chern numbers. Such a QAH junction may function as a chiral edge current distributer at zero magnetic field, but its realization remains challenging. Here, by employing an in-situ mechanical mask, we use molecular beam epitaxy to synthesize QAH insulator junctions, in which two QAH insulators with different Chern numbers are connected along a one-dimensional junction. For the junction between Chern numbers of 1 and -1, we observe quantized transport and demonstrate the appearance of the two parallel propagating chiral interface channels along the magnetic domain wall at zero magnetic field. For the junction between Chern numbers of 1 and 2, our quantized transport shows that a single chiral interface channel appears at the interface. Our work lays the foundation for the development of QAH insulator-based electronic and spintronic devices and topological chiral networks.

  View details for DOI 10.1038/s41467-023-36488-y

  View details for Web of Science ID 001188339600001

  View details for PubMedID 36765068

  View details for PubMedCentralID PMC9918724

• Environmental Doping-Induced Degradation of the Quantum Anomalous Hall Insulators NANO LETTERS Tay, H., Zhao, Y., Zhou, L., Zhang, R., Yan, Z., Zhuo, D., Chan, M. H. W., Chang, C. 2023; 23 (3): 1093-1099

  Abstract

  The quantum anomalous Hall (QAH) insulator carries dissipation-free chiral edge current and thus provides a unique opportunity to develop energy-efficient transformative information technology. Despite promising advances, the QAH insulator has thus far eluded any practical applications. In addition to its low working temperature, the QAH state in magnetically doped topological insulators usually deteriorates with time in ambient conditions. In this work, we store three QAH devices with similar initial properties in different environments. The QAH device without a protection layer in air shows clear degradation and becomes hole-doped. The QAH device kept in an argon glovebox without a protection layer shows no measurable degradation after 560 h, and the device protected by a 3 nm AlOx protection layer in air shows minimal degradation with stable QAH properties. Our work shows a route to preserve the dissipation-free chiral edge state in QAH devices for potential applications in quantum information technology.

  View details for DOI 10.1021/acs.nanolett.2c04871

  View details for Web of Science ID 000926712400001

  View details for PubMedID 36715442

• Zero Magnetic Field Plateau Phase Transition in Higher Chern Number Quantum Anomalous Hall Insulators PHYSICAL REVIEW LETTERS Zhao, Y., Zhang, R., Zhou, L., Mei, R., Yan, Z., Chan, M. H. W., Liu, C., Chan, C. 2022; 128 (21): 216801

  Abstract

  The plateau-to-plateau transition in quantum Hall effect under high magnetic fields is a celebrated quantum phase transition between two topological states. It can be achieved by either sweeping the magnetic field or tuning the carrier density. The recent realization of the quantum anomalous Hall (QAH) insulators with tunable Chern numbers introduces the channel degree of freedom to the dissipation-free chiral edge transport and makes the study of the quantum phase transition between two topological states under zero magnetic field possible. Here, we synthesized the magnetic topological insulator (TI)/TI pentalayer heterostructures with different Cr doping concentrations in the middle magnetic TI layers using molecular beam epitaxy. By performing transport measurements, we found a potential plateau phase transition between C=1 and C=2 QAH states under zero magnetic field. In tuning the transition, the Hall resistance monotonically decreases from h/e^{2} to h/2e^{2}, concurrently, the longitudinal resistance exhibits a maximum at the critical point. Our results show that the ratio between the Hall resistance and the longitudinal resistance is greater than 1 at the critical point, which indicates that the original chiral edge channel from the C=1 QAH state coexists with the dissipative bulk conduction channels. Subsequently, these bulk conduction channels appear to self-organize and form the second chiral edge channel in completing the plateau phase transition. Our study will motivate further investigations of this novel Chern number change-induced quantum phase transition and advance the development of the QAH chiral edge current-based electronic and spintronic devices.

  View details for DOI 10.1103/PhysRevLett.128.216801

  View details for Web of Science ID 000808312000011

  View details for PubMedID 35687436