Light-induced phase crossovers in a quantum spin Hall system

Abstract

In this work, we theoretically investigate the light-induced topological phases and finite-size crossovers in a paradigmatic quantum spin Hall (QSH) system with high-frequency pumping optics. Taking the HgTe quantum well for example, our numerical results show that circularly polarized light can break time-reversal symmetry and induce the quantum anomalous Hall (QAH) phase. In particular, the coupling between the edge states is spin dependent, and it is related not only to the size of the system but also to the strength of the polarized pumping optics. By tuning the two parameters (system width and optical pumping strength), we obtain four transport regimes, namely QSH, QAH, edge conducting, and normal insulator. These four different transport regimes have contrasting edge conducting properties which will feature prominently in transport experiments on various topological materials.