Light-induced phase crossovers in a quantum spin Hall system

TL;DR

This paper theoretically explores how high-frequency circularly polarized light can induce topological phase transitions in quantum spin Hall systems, revealing controllable regimes including QSH, QAH, and insulators.

Contribution

It demonstrates the light-induced transition from QSH to QAH phase and identifies how system size and optical strength control edge state coupling and transport regimes.

Findings

Circularly polarized light induces QAH phase in HgTe quantum wells.

Edge state coupling depends on system size and optical pumping strength.

Four distinct transport regimes are identified and characterized.

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 an 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 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.