Rydberg Excitons and Trions in Monolayer MoTe2

Monolayer transition metal dichalcogenide (TMDC) semi-conductors exhibit strong excitonic optical resonances, which serve as a microscopic, noninvasive probe into their fundamental properties. Like the hydrogen atom, such excitons can exhibit an entire Rydberg series of resonances. Excitons have been extensively studied in most TMDCs (MoS2, MoSe2, WS2, and WSe2), but detailed exploration of excitonic phenomena has been lacking in the important TMDC material molybdenum ditelluride (MoTe2). Here, we report an experimental investigation of excitonic luminescence properties of monolayer MoTe2 to understand the excitonic Rydberg series, up to 3s. We report a significant modification of emission energies with temperature (4 to 300 K), thereby quantifying the exciton- phonon coupling. Furthermore, we observe a strongly gate-tunable exciton- trion interplay for all the Rydberg states governed mainly by free-carrier screening, Pauli blocking, and band gap renormalization in agreement with the results of first-principles GW plus Bethe- Salpeter equation approach calculations. Our results help bring monolayer MoTe2 closer to its potential applications in near-infrared optoelectronics and photonic devices.