Nanophotonic chiral coupling to gate-controlled excitons in monolayer WSe2*

Atomically thin semiconductors exhibit pronounced optical responses governed by excitonic resonances, which can be modulated significantly via electrostatic doping. Moreover, their valley character gives rise to circularly polarized optical transitions. The evanescent chirality, then, of tightly confined waveguide modes enables direction-dependent coupling of nanophotonic near-fields to these electrically tunable excitons. Here, we fabricate a gate-controlled van der Waals heterostructure of encapsulated monolayer tungsten diselenide (WSe2) interfaced with a low-loss, high-index titanium dioxide waveguide. We characterize gate-modified directional coupling of exciton emission into the waveguide, which is spectrally resolved to identify peak-dependent chiral coupling efficiencies. This work broadens our understanding of exciton states in two-dimensional materials well-suited for future integration in on-chip photonic technologies.