Institute for Nanoelectronic Devices and Quantum Computing, Fudan University

报告摘要:

It remains highly desirable to achieve a robust quantum anomalous Hall (QAH) state, i.e., the quantized Hall effect in the absence of external magnetic field, for its potential applications in energy-efficient electronic devices and topological quantum computing. In this regard, the stoichiometric magnetic topological insulator MnBi₂Te₄emerges as a cleaner and more robust platform to realize QAH and other magnetic topological phases than its magnetically doped counterpart. However, the Hall quantization at zero field is scarcely observed in transports in odd-layer MnBi₂Te₄¹, whereas the character of the axion insulator state of even-layer MnBi₂Te₄is debated given the recent experimental report of a metallic edge state in such a phase^2-4. This presentation will provide microscopic insights into these issues by revealing the critical role of disorders in realizing both QAH and the axion insulator state of MnBi₂Te₄. By utilizing various scanning probe microscopes, we attribute the observed metallic edge state of even-layer MnBi₂Te₄to the disorder-induced spectrum broadening of a gapped helical edge state. We also attribute the quantization breakdown at zero field of odd-layer MnBi₂Te₄to a finite bulk conductivity and disorder-induced bulk-edge scattering. In molecular beam epitaxy grown MnBi2Te4 thin films, a quantized Hall insulator scenario is proposed to explain a large dissipation in the quantized Hall state. These results reshape our current understanding of magnetic topological phases in MnBi₂Te₄.

Reference:

1 Deng, Y. J.et al. Quantum anomalous Hall effect in intrinsic magnetic topological insulator MnBi₂Te₄.Science367, 895-900, (2020).

2 Lin, W.et al. Direct visualization of edge state in even-layer MnBi₂Te₄at zero magnetic field.Nature Communications13, 7714, (2022).

3 Feng, Y.et al. Helical Luttinger Liquid on the Edge of a Two-Dimensional Topological Antiferromagnet.Nano Lett22, 7606-7614, (2022).

4 Li, Y. X.et al. Giant nonlocal edge conduction in the axion insulator state of MnBi₂Te₄.Sci Bull68, 1252-1258, (2023).

报告人简介:

Dr. Xiaodong Zhou obtained his Ph. D. in 2014 from Tsinghua University and was a postdoctoral researcher at Columbia University from 2014 to 2017. He has been an assistant professor in the Institute for Nanoelectronic Devices and Quantum Computing (INQC) of Fudan University since 2017. His research is to use various scanning probe techniques (scanning microwave impedance microscopy, magnetic force microscopy and scanning tunneling microscopy) to study the electronic and magnetic structures of quantum materials at microscopic scale, ranging from high Tc superconductors, strongly correlated oxide thin films and magnetic topological materials.

邀请人：朱诗雨副研究员（82648049）