Fully tuneable Bloch-Band polaritons emerging from WS2 monolayer excitons in an optical lattice at room temperature

The engineering of non-linear light-matter states in optical lattices has emerged as a key research strategy for the exploration of Hamiltonians in the spirit of ultrafast- and possibly quantum-simulation. It furthermore has revealed its potential to probe non-trivial topology phenomena. Excitons in atomically thin crystals have emerged as an ideal active medium for such purposes, since they couple strongly with light, and bear the potential to harness giant non-linearities and interactions. In this work, we present a pioneering experiment conducted at room temperature in an open optical cavity of high quality, with an implemented one-dimensional photonic lattice (see Fig. 1a ). Such optical microstructure has been utilized recently in experiments addressing Bloch-mode condensates using fluorescent proteins [1] . In our present work, however, we integrate an atomically thin layer of WS 2 in such a device [2] . We discuss the strong-to-weak coupling crossover, and highlight the emergence of a lattice-band-structure in the tight-binding configuration at room temperature, fuelled by the emission from monolayer excitons ( Fig. 1b ).