Biexciton fine structure in monolayer transition metal dichalcogenides

TL;DR

This paper investigates the fine structure of biexcitons in monolayer transition metal dichalcogenides, revealing a distinct electron-hole exchange-induced splitting through ultrafast spectroscopy and microscopic theory, advancing understanding of Coulomb complexes.

Contribution

It provides the first detailed experimental and theoretical analysis of biexciton fine structure in monolayer TMDCs, highlighting electron-hole exchange effects.

Findings

Biexcitons exhibit a meV-scale fine structure due to electron-hole exchange.

Ultrafast pump-probe experiments confirm biexciton signatures and fine structure.

The study offers a new pathway to accurately access biexciton spectra.

Abstract

The optical properties of atomically thin transition metal dichalcogenide (TMDC) semiconductors are shaped by the emergence of correlated many-body complexes due to strong Coulomb interaction. Exceptional electron-hole exchange predestines TMDCs to study fundamental and applied properties of Coulomb complexes such as valley depolarization of excitons and fine-structure splitting of trions. Biexcitons in these materials are less understood and it has been established only recently that they are spectrally located between exciton and trion. Here we show that biexcitons in monolayer TMDCs exhibit a distinct fine structure on the order of meV due to electron-hole exchange. Ultrafast pump-probe experiments on monolayer WSe$_2$ reveal decisive biexciton signatures and a fine structure in excellent agreement with a microscopic theory. We provide a pathway to access biexciton spectra with unprecedented accuracy, which is valuable beyond the class of TMDCs, and to understand even higher Coulomb complexes under the influence of electron-hole exchange.