CSU makes new progress on Chen-tunable quantum anomalous Hall effect

Recently, the International Center for Quantum Functional Materials Design at the National Research Center for Microscale Matter Science, University of Science and Technology of China, Hefei, and Professor Zhenhua Qiao's research group in the Department of Physics have discovered a theoretically stale tunable quantum anomalous Hall effect based on monolayer transition metal oxides.

The results were published on July 14, 2022 in Physical Review Letters [Phys. Rev. Lett. 129, 036801 (2022)], a leading international academic journal in physics, and were selected as the cover of the current issue. The first author of the paper is Zeyu Li, a 2022 Ph.

The quantum Hall effect is a dissipation-free quantum transport property due to quantization of Landau energy levels in an externally reinforced magnetic field. However, the need for an externally reinforced magnetic field greatly limits the practical application prospects of this effect. In recent decades, the exploration of the quantum Hall effect without magnetic field (i.e., quantum anomalous Hall effect) has attracted the attention of many physicists and has made great progress both theoretically and experimentally.

Currently, the proposed or realized quantum anomalous Hall effect is concentrated in the systems with small stale number of 1 (based on magnetic topological insulator films, etc.) or 2 (based on monolayer graphene, etc.), and the size of stale number directly corresponds to the number of quantum channels, and the status of low stale number significantly affects the efficiency of quantum anomalous Hall devices. In the exploration of large or tunable quantum anomalous Hall effect, researchers have mainly used the means of controlling the thickness of magnetic topological insulator films or the concentration of magnetic doping to achieve quantum anomalous Hall effect with different stales. It is important to note that in all these systems, once the sample or device is prepared, the stale size of the corresponding quantum anomalous Hall effect is also uniquely determined.

Fig: Distribution and energy spectrum of the Berry curvature of monolayer PdSbO3. (a-b) magnetization direction along x-axis; (c-d) magnetization direction along z-axis. (The present legend is completely independent of QAHE and Chen number)

In the present work, the group has systematically investigated and found that the quantum anomalous Hall effect of different stales can be achieved on the monolayer transition metal oxide materials NiAsO3 and PdSbO3 by modulating the magnetization direction of the materials through the application of a weak magnetic field. It is found that both materials have six spin-polarized Dirac points at the Fermi energy level. After the introduction of spin-orbit coupling, each Dirac point contributes half a quantum of Hall conductance, but in different directions. When the magnetization direction is in-plane and breaks the vertical mirror symmetry, four of the Dirac points have the same Berry curvature, while the remaining two Dirac points have opposite Berry curvature; at this point, the system has a quantum anomalous Hall effect with Chen number 1. When the magnetization direction deviates from the system plane, the six Dirac points contribute the same Berry curvature. In this case, the system has a quantum anomalous Hall effect with a cohort of 3. This study not only provides a new material platform to study the quantum anomalous Hall effect, but also reveals the existence and physical causes of the quantum anomalous Hall effect with a tunable age.

This work was supported by the National Natural Science Foundation of China, Anhui Province, the University Research Department and the University Human Resources Department.

Link to the paper：

https://link.aps.org/doi/10.1103/PhysRevLett.129.036801