Floquet Engineering of Topological Phase Transitions in Intrinsic Ferrovalley Semiconductor via Circularly and Elliptically Polarized Light

Abstract

Floquet engineering provides a non-contact approach to dynamically tailor electronic band structures and induce topological phase transitions via time-periodic optical fields. However, experimental limitations such as dissipation and the underexplored role of anisotropic driving have hindered its application in two-dimensional magnetic semiconductors. Recently, monolayer 2H RuCl₂ has been identified as a promising ferrovalley material exhibiting large out-of-plane magnetic anisotropy and tunable first-and second-order topological phases. In this work, we construct a Wannier-based tight-binding model and apply Floquet-Bloch theory to monolayer 2H RuCl₂ under circularly, elliptically, and linearly polarized light. We examine both off-resonant and on-resonant driving schemes by considering different scales of light frequency. In the off-resonant scheme, we demonstrate that both the amplitude and ellipticity of light can trigger band inversion at the K' valley, leading to a topological phase transition into a quantum anomalous Hall (QAH) phase with a quantized Hall conductance and Chern number C = 1. In the on-resonant scheme, the hybridization of Floquet replica bands reveals even richer topological phase transitions driven by light frequency, amplitude, and ellipticity. Notably, we observe a Floquet-induced QAH phase with high Chern number C = 3, suggesting that intrinsic ferrovalley semiconductors such as RuCl₂ serve as an ideal platform for Floquet band engineering in future topological quantum devices.