Multiple magnetic states, valley electronics, and topological phase transitions in two-dimensional Janus XYZH monolayers and bilayers
Phys. Rev. B 112, 035413 – Published 14 July, 2025
DOI: https://doi.org/10.1103/9ctn-39n5
Abstract
Exploring the coupling between layer, magnetism, valley, and topology in two-dimensional (2D) materials is an important approach to deepen our understanding of materials properties. We propose 27 stable ferromagnetic monolayers of Janus XYZH . All these monolayers exhibit spontaneous valley polarization, forming ferromagnetic valley (FV) monolayers, showing the anomalous valley Hall (AVH) effect. By applying external strain, the topological phase transitions including quantum anomalous Hall (QAH) effect can be introduced. In the ScBrSH bilayer system, AA and AB stacking configurations were constructed through interlayer sliding and rotating operations. The bilayer system exhibits interlayer antiferromagnetic ordering with spontaneous valley polarization differing from the FV observed in monolayers. The sliding ferroelectricity in the AA stacking bilayer indicates that the system exhibits pronounced multiferroic characteristics. Further analysis shows that interlayer sliding can introduce a layer polarization anomalous valley Hall (LPAVH) effect, which can be precisely controlled by tuning the direction of the ferroelectric polarization. Upon applying external strain, the quantum layer spin Hall effect observed during the topological phase transition in the bilayer can be regarded as the superposition of two QAH monolayers. Furthermore, applying a twisting operation to the bilayer induces unexpected altermagnetism. Our study systematically reveals the rich physical properties of 2D XYZH materials, providing important theoretical foundations and guidance for the design and development of next-generation quantum devices.
