Electrically controllable chirality in a nanophotonic interface with a two-dimensional semiconductor

Researchers demonstrate electrically controllable chirality by exploiting doping-dependent valley polarization of excitonic states in monolayer tungsten diselenide. Chiral nanophotonic interfaces enable propagation direction-dependent interactions between guided optical modes and circularly dichroic materials. Electrical tuning of interface chirality would aid active, switchable non-reciprocity in on-chip optoelectronic and photonic circuitry, but remains an outstanding challenge. Here, we report electrically controllable chirality in a nanophotonic interface with atomically thin monolayer tungsten diselenide (WSe2). Titanium dioxide waveguides are directly fabricated on the surface of low-disorder, boron nitride-encapsulated WSe2. Following integration, photoluminescence from excitonic states into the waveguide can be electrically switched between balanced and directionally biased emission. The operational principle leverages the doping-dependent valley polarization of excitonic states in WSe2. Furthermore, the nanophotonic waveguide can function as a near-field source for diffusive exciton fluxes, which display valley and spin polarizations that are inherited from the interface chirality. Our versatile fabrication approach enables the deterministic integration of photonics with van der Waals heterostructures and could provide optical control over their excitonic and charge-carrier behaviour.