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

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.