Charge control of excitons in a novel Janus TMD 2D-material device

Janus transition metal dichalcogenides (TMDs) have different chalcogens on the two surfaces of the monolayer, which creates an inherent out-of-plane asymmetry. This provides an inbuilt electric field within a single monolayer and therefore holds the promise of exploiting the long-range interactions between dipolar excitons, without the complexity of building TMD heterostructures. Recent work has shown the synthesis of Janus TMDs, but the optical quality has hindered the identification of the excitonic states. In this talk, I will present our work on the first integration of a Janus WSeS monolayer into a fully encapsulated, charge-controllable device. Encapsulation in hexagonal boron nitride results in the narrowest photoluminescence linewidths reported to date (< 10 meV at 4 K), while gate-dependent reflection contrast measurements allow for the assignment of the neutral exciton and negatively charged trions. We measure a similar exchange energy splitting (7 meV) between the inter- and intra-valley negative trions as for conventional TMDs and magnetic field dependent measurements show that the exciton g-factors agree with our theoretical predictions. These results demonstrate that Janus TMDs are suitable for integration into optoelectronic devices and quantum optics applications.