Inducing room-temperature valley polarization of excitonic emission in transition metal dichalcogenide monolayers

TL;DR

This study demonstrates that high levels of electron doping in transition metal dichalcogenide monolayers can induce significant valley polarization at room temperature, advancing the development of practical valleytronic devices.

Contribution

It shows that strong electron doping induces substantial valley polarization in TMD monolayers at room temperature, overcoming thermal depolarization effects.

Findings

Achieved 61% valley contrast in tungsten diselenide at room temperature.

Achieved 37% valley contrast in molybdenum diselenide at room temperature.

Charged excitons can serve as quantum units for valleytronic devices.

Abstract

The lowest energy states in transition metal dichalcogenide (TMD) monolayers follow valley selection rules, which have attracted vast interest due to the possibility of encoding and processing of quantum information. However, these quantum states are strongly affected by the temperature-dependent intervalley scattering causing complete valley depolarization, which is hampering any practical applications of TMD monolayers at room temperature. Therefore, for achieving clear and robust valley polarization in TMD monolayers one needs to suppress parasitic depolarization processes, which is the central challenge in the growing field of valleytronics. Here, in electron-doping experiments on TMD monolayers, we demonstrate that strong doping levels beyond $10^{13}$~cm$^{-2}$ can induce 61\% and 37\% valley contrast at room temperature in tungsten diselenide and molybdenum diselenide monolayers, respectively. Our results indicate that charged excitons in TMD monolayers can be utilized as quantum units in designing of practical valleytronic devices operating at 300 K.