Photoinduced topological phase transition in monolayer 1T$^\prime$-MoS$_2$

TL;DR

This paper explores how high-frequency circularly polarized light can induce and control topological phase transitions in monolayer 1T'--MoS2, revealing a variety of light-driven topological states.

Contribution

It introduces a theoretical framework combining a low-energy Hamiltonian with Floquet theory to predict light-induced topological phases in monolayer MoS2.

Findings

Identification of light-controlled topological transitions with gap closings.

Demonstration of switching between quantum spin Hall and quantum Hall phases.

Prediction of tunable topological phases via circularly polarized light.

Abstract

We investigate the nonequilibrium topological phases of monolayer 1T$^\prime$--MoS$_2$ under high-frequency circularly polarized driving using a low-energy $k\!\cdot\!p$ Hamiltonian combined with a van Vleck expansion. The off-resonant field generates spin- and valley-dependent mass corrections that reshape the Berry curvature profile and shift the conditions for band inversion. By evaluating the quasienergy bands, Berry curvatures, Hall conductivities, and spin- valley-resolved Chern numbers, we identify a sequence of light-controlled topological transitions marked by well-defined gap closings. Depending on the Floquet coupling strength and the electric-field parameter, the system evolves between the equilibrium quantum spin Hall (QSH) state and a set of driven phases including spin-polarized quantum Hall insulator (S-QHI), quantum valley Hall (QVH or BI) and photo-induced quantum Hall insulator (P-QHI) regimes. The results establish 1T$^\prime$--MoS$_2$ as a tunable platform where circular driving selectively manipulates spin and valley degrees of freedom, enabling controlled access to non-equilibrium topological phases in transition-metal dichalcogenides.