Neutral and Charged Inter-Valley Biexcitons in Monolayer MoSe$_2$

TL;DR

This study uses advanced spectroscopy to identify and characterize neutral and charged inter-valley biexcitons in monolayer MoSe2, revealing their energies and quantum pathways, with implications for optoelectronic applications.

Contribution

It provides the first unambiguous identification of inter-valley biexcitons in monolayer MoSe2 using polarization-resolved two-dimensional spectroscopy and theoretical modeling.

Findings

Identification of neutral inter-valley biexciton with ~20 meV binding energy

Detection of charged inter-valley biexciton with ~5 meV binding energy

Elucidation of quantum pathways responsible for biexciton formation

Abstract

In atomically thin transition metal dichalcogenides (TMDs), reduced dielectric screening of the Coulomb interaction leads to strongly correlated many-body states, including excitons and trions, that dominate the optical properties. Higher-order states, such as bound biexcitons, are possible but are difficult to identify unambiguously using linear optical spectroscopy methods alone. Here, we implement polarization-resolved two-dimensional coherent spectroscopy to unravel the complex optical response of monolayer MoSe$_2$ and identify multiple higher-order correlated states. Decisive signatures of neutral and charged inter-valley biexcitons appear in cross-polarized two-dimensional spectra as distinct resonances with respective ~20 meV and ~5 meV binding energies--similar to recent calculations using variational and Monte Carlo methods. A theoretical model taking into account the valley-dependent optical selection rules reveals the specific quantum pathways that give rise to these states. Inter-valley biexcitons identified here, comprised of neutral and charged excitons from different valleys, offer new opportunities for creating exotic exciton-polariton condensates and for developing ultrathin biexciton lasers and polarization-entangled photon sources.