All-Optical Materials Design of Chiral Edge Modes in Transition-Metal Dichalcogenides

TL;DR

This paper demonstrates how optical pumping of monolayer transition-metal dichalcogenides can induce topologically protected chiral edge modes through non-equilibrium phase transitions, relying on symmetry and intrinsic band structure.

Contribution

It introduces a novel method to engineer chiral edge modes in TMDCs using optical pumping and symmetry principles, supported by ab initio calculations.

Findings

Photo-induced band inversions depend linearly on pump field.

Transition from one to two chiral edge modes with detuning.

Control of edge modes is symmetry-driven and material-insensitive.

Abstract

Manipulating materials properties far from equilibrium recently garnered significant attention, with experimental emphasis on transient melting, enhancement, or induction of electronic order. A more tantalizing aspect of the matter-light interaction regards the possibility to access dynamical steady states with distinct non-equilibrium phase transitions to affect electronic transport. Here, we show that the interplay of crystal symmetry and optical pumping of monolayer transition-metal dichalcogenides (TMDCs) provides a novel avenue to engineer topologically-protected chiral edge modes. In stark contrast to graphene and previously-discussed toy models, the underlying generic mechanism relies on the intrinsic three-band nature of TMDCs near the band edges. Photo-induced band inversions scale linearly in applied pump field and exhibit a transition from one to two chiral edge modes upon sweeping from red to blue detuning. We develop a strategy to understand non-equilibrium Floquet-Bloch bands and topological transitions directly from ab initio calculations, and illustrate for the example of WS$_2$ that control of chiral edge modes can be dictated solely from symmetry principles and is not qualitatively sensitive to microscopic materials details.