Direct Measurement of the Radiative Pattern of Bright and Dark Excitons and Exciton Complexes in Encapsulated Tungsten Diselenide

TL;DR

This study directly measures the radiation patterns of bright and dark excitons, including grey excitons, in encapsulated tungsten diselenide, revealing their distinct optical emission characteristics at cryogenic temperatures.

Contribution

It provides the first direct measurement of the radiative pattern of grey excitons in encapsulated WSe2 monolayers, advancing understanding of dark exciton properties.

Findings

Grey excitons have a distinct radiation pattern from bright excitons.

The radiation pattern of dark excitons deviates significantly from that of bright excitons.

Encapsulation enhances the optical quality, enabling direct measurement.

Abstract

The optical properties of particularly the tungsten-based transition-metal dichalcogenides are strongly influenced by the presence of dark excitons. Recently, theoretical predictions as well as indirect experimental insights have shown that two different dark excitons exist within the light cone. While one is completely dark, the other one is only dipole forbidden out-of-plane, hence referred to as grey exciton. Here, we present angle-resolved spectroscopic data of a high-quality hexagonal-BN-encapsulated WSe2 monolayer with which we directly obtain the radiation pattern of this grey exciton that deviates from that of the bright exciton and other exciton complexes obtained at cryogenic temperatures.