Research

Physical Review Letters reports Professor Xie Xin-Cheng's research in quantum anomalous Hall effect

JAN . 25 2019
Peking University, Jan. 25, 2019: Professor Xie Xin-Cheng from International Center for Quantum Materials (ICQM), School of Physics, Peking University, visitor Professor Chui-Zhen Chen from Soochow University and Professor Liu Haiwen from Beijing Normal University recently made an important research progress in quantum anomalous Hall (QAH) effect. They found that the absence of structure inversion symmetry in present experimental QAH systems can give rise to a new type of critical line, i.e. a Berezinskii-Kosterlitz-Thouless (BKT)-type transition, during the Hall conductance plateau switching. The results have been published online on Jan. 15th in Phys. Rev. Lett.122, 026601(2019).

QAH insulator is a new state of quantum matter and important for both its fundamental and application values. Plateau transitions between different quantization Hall conductance features topological properties of QAH effect, and represents an important type of experimentally feasible quantum phase transition. It is widely believed that Hall plateaus transition in QAH belongs to the universality class of traditional quantum Hall plateau transition. However, recent experiments show that the critical exponents and temperature dependence of Hall conductance are deviated from universal value of the quantum Hall plateau transition. Moreover, unlike quantum Hall insulator, the QAH insulator has the zero Hall plateau with random magnetic domains. Therefore, it is crucial and also of practical significance to understand how the zero Hall plateau state is affected by random domains in the presence of various types of disorder.

(a) Phase diagram of magnetic TI on the plane of diagonal disorder strength W and spatial-
averaged normalized magnetization
Mz(r)/ Ms. The spin Chern insulator (spin CI), Chern insulator (CI), and normal insulator (NI) are separated by a critical point or a critical region. (b) shows disorder-averaged Hall conductance σxy and renormalized localization length Λ as a function of magnetization Mz(r)/ Ms.

In this work, the authors study the effects of random domains on a magnetic TI thin film by exact numerical simulations. They find that the structure inversion symmetry plays a determinant role for the scaling behavior of QAH plateau transition. With structure inversion symmetry, the system decouples into two subsystems, which are topological equivalent to two Chern insulators with opposite Chern numbers. Subsequently, the system presents the traditional quantum-Hall criticality with single critical point. On the other hand, the absence of structure inversion symmetry, which is common case in present experimental QAH systems, can give rise to mixture between the two subsystems, and results in a new type of critical line. Scaling analysis supports the latter case without structure inversion symmetry belongs to a new universality class: the BKT-type transition. This prediction can be verified in future transport experiments.

This work is supported by the National Basic Research Program of China, the Strategic Priority Research Program of Chinese Academy of Sciences, the Fundamental Research Funds for the Central Universities, HKRGC and Croucher Foundation and Croucher Innovation.

Edited by: Huang Weijian
Source: International Center for Quantum Materials