Floquet-engineered Valley Topology with Anisotropic Response in 1T'-WSe$_2$ and Janus WSeTe monolayers

TL;DR

This paper explores how periodic light can induce topological phase transitions in anisotropic 1T'-WSe$_2$ and Janus WSeTe monolayers, revealing valley-specific and anisotropic responses useful for valleytronics.

Contribution

It demonstrates Floquet-driven topological phase transitions in WSe$_2$ and WSeTe monolayers, highlighting valley-specific and anisotropic effects with potential device applications.

Findings

Single TPT from QSH to QAH in 1T'-WSe$_2$

Two-stage Floquet TPT in WSeTe with valley-polarized intermediate phase

Predicted anisotropic response under oblique light incidence

Abstract

Valley topology has emerged as a key concept for realizing new classes of quantum states. Here, we investigate Floquet-engineered topological phase transitions in anisotropic 1T'-WSe$_2$ and its Janus derivative WSeTe monolayers, which exhibit valley-degenerate and valley-polarized characteristics, respectively. In 1T'-WSe$_2$, a single topological-phase-transition (TPT) occurs from the quantum-spin-Hall state (QSH) to the quantum anomalous Hall (QAH) state, involving one spin channel at both valleys simultaneously. In contrast, Janus WSeTe undergoes a two-stage Floquet-driven TPT that occurs within a single valley and sequentially involves two spin components. The intermediate phase manifests as a valley-polarized QAH (vp-QAH) state with a finite valley Chern number, while the final phase evolves into a high-Chern-number QAH state with distinct valley gaps. Furthermore, an in-plane anisotropic response of the TPTs is predicted under oblique light incidence, reflecting the intrinsic low-symmetry nature of the lattice. These findings provide a comprehensive understanding of Floquet-engineered valley-based topological properties and offer guidance for designing light-controllable valleytronic and topological devices.