Cascaded emission of single photons from the biexciton in monolayered WSe2

TL;DR

This study demonstrates the existence of a localized biexciton in monolayer WSe2, which produces a cascaded emission of single photons, advancing quantum optics applications with 2D materials.

Contribution

First unambiguous demonstration of a localized biexciton in monolayer WSe2, confirming its role in cascaded single-photon emission.

Findings

Identification of biexciton via time-resolved photoluminescence

Observation of superlinear emission and polarization features

Cross-correlation confirms cascaded photon emission

Abstract

Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, since they benefit from enormous coulomb correlations between electrons and holes. Especially in WSe2, sharp emission features have been observed at cryogenic temperatures, which act as single photon sources . Tight exciton localization has been assumed to induce an anharmonic excitation spectrum, however, the evidence of the hypothesis, namely the demonstration of a localized biexciton, is elusive. Here, we unambiguously demonstrate the existence of a localized biexciton in a monolayer of WSe2, which triggers an emission cascade of single photons. The biexciton is identified by its time-resolved photoluminescence, superlinearity and distinct polarization in micro-photoluminescence experiments. We evidence the cascaded nature of the emission process in a cross-correlation experiment, which yields a strong bunching behavior. Our work paves the way to a new generation of quantum optics experiments with two-dimensional semiconductors.