Cascaded emission of single photons from the biexciton in monolayered WSe2.

Yu-Ming He,Christian Schneider,Sven Höfling,Vasilij Baumann,Oliver Iff,Kartik Srinivasan,Marcelo Davanco,Nils Lundt

doi:10.1038/ncomms13409

Abstract

Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, as 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 behaviour. Our work paves the way to a new generation of quantum optics experiments with two-dimensional semiconductors.

Highlights

Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, as they benefit from enormous Coulomb correlations between electrons and holes
Transition metal dichalcogenides semiconductors have emerged as a new platform to study excitonic effects in two dimensions[6,7,8,9,10], in particular as they benefit from enormous Coulomb correlations between electrons and holes as a result of reduced dielectric screening[11,12,13] and feature unique spinor properties[14]
Strong progress has been made in studying excitonic effects in two-dimensional materials, including the exploration of the valley pseudospin dynamics[14,15], valley polarization control[16,17,18,19,20] and strong coupling effects[21,22]

Summary

Introduction

Monolayers of transition metal dichalcogenide materials emerged as a new material class to study excitonic effects in solid state, as they benefit from enormous Coulomb correlations between electrons and holes. Single photon emission from localized states in monolayers of transition metal dichalcogenides has recently been observed[23,24,25,26,27], the characteristic feature that determines an anharmonic excitation spectrum in an excitonic system, which is a well-isolated biexcitonic state, has not been observed. Delocalized biexcitonic states in WSe2 have been attributed to a superlinearly increasing, broad emission feature on the lowenergy side of the characteristic excitonic resonance[28].

Results

Conclusion