Biexcitons fine structure and non-equilibrium effects in transition metal dichalcogenides monolayers from first principles

Transition metal dichalcogenides monolayers host strongly bounded Coulomb complexes such as exciton and trion due to charge confinement and screening reduction in two dimensions. Biexciton, a bound state of two electrons and two holes, has also been observed in these materials with a binding energy which is one order of magnitude larger than its counterpart in conventional semiconductors. Here, using first principles methods, we address the biexciton in WSe2 monolayer and unravel the important role of the electron-hole exchange interaction in dictating the valley character of biexciton states and their fine structure. In particular, the fundamental biexciton transition which is located between the exciton and trion peaks is shown to have a fine structure of 2.8 meV mainly due to the splitting of the dark exciton state under the intervalley electron-hole exchange interaction. Non equilibrium effects are also addressed and optical fingerprints of non-thermalized biexciton population are discussed. The reduced dimensions of 2D materials make them an ideal platform to realise quantum many-body effects such as the formation of exciton complexes. Here, using first principles calculations the authors investigate biexcitons in WSe2 monolayers and uncover the role electron-hole exchange interaction plays in the valley characteristics of the biexciton.

Automated summary

Transition metal dichalcogenides monolayers can host strongly bounded Coulomb complexes like excitons and trions, with biexcitons having a binding energy one order of magnitude higher than conventional semiconductors. Using first principles methods, researchers have investigated biexcitons in WSe2 monolayers and highlighted the crucial role of the electron-hole exchange interaction in determining the valley characteristics of the biexciton states.