Revealing the Biexciton and Trion-exciton Complexes in BN Encapsulated WSe2

TL;DR

This study uses low-temperature photoluminescence spectroscopy to identify and analyze biexciton and trion-exciton complexes in BN-encapsulated WSe2, clarifying their binding energies and charge dependencies for quantum optoelectronics.

Contribution

It provides the first experimental identification of the biexciton state in charge-neutral WSe2 and clarifies its existence only in this state, resolving previous discrepancies.

Findings

Biexciton exists only in charge-neutral WSe2.

Light electron doping leads to trion-exciton formation.

Enhanced understanding of many-body excitonic complexes in TMDs.

Abstract

Strong Coulomb interactions in single-layer transition metal dichalcogenides (TMDs) result in the emergence of strongly bound excitons, trions and biexcitons. These excitonic complexes possess the valley degree of freedom, which can be exploited for quantum optoelectronics. However, in contrast to the good understanding of the exciton and trion properties, the binding energy of the biexciton remains elusive, with theoretical calculations and experimental studies reporting discrepant results. In this work, we resolve the conflict by employing low-temperature photoluminescence spectroscopy to identify the biexciton state in BN encapsulated single-layer WSe2. The biexciton state only exists in charge neutral WSe2, which is realized through the control of efficient electrostatic gating. In the lightly electron-doped WSe2, one free electron binds to a biexciton and forms the trion-exciton complex. Improved understanding of the biexciton and trion-exciton complexes paves the way for exploiting the many-body physics in TMDs for novel optoelectronics applications.