Symmetry-dependent exciton-exciton interaction and intervalley biexciton in monolayer transition metal dichalcogenides

TL;DR

This paper develops a theoretical model to describe exciton interactions in monolayer TMDs, revealing how symmetry influences exciton coupling and the formation of intervalley biexcitons, with implications for understanding their energy structure.

Contribution

It introduces a unified exciton Hamiltonian considering symmetry-dependent interactions, explaining the formation and energy of intervalley biexcitons in monolayer TMDs.

Findings

Exciton interactions depend on their symmetry, mostly repulsive except for intervalley cases.

Intervalley excitons attract, leading to biexciton formation.

Biexciton binding energy relates to exciton mass and dielectric environment.

Abstract

The multivalley band structure of monolayer transition metal dichalcogenides (TMDs) gives rise to intravalley and intervalley excitons. Much knowledge of these excitons has been gained, but fundamental questions remain, such as how to describe them all in a unified picture with their correlations, how are those from different valleys coupled to form the intervalley biexciton? To address the issues, we derive an exciton Hamiltonian from interpair correlations between the constituent carriers-fermions of two excitons. Identifying excitons by irreducible representations of their point symmetry group, we find their pairwise interaction depending on interacting excitons' symmetry. It is generally repulsive, except for the case excitons from different valleys, which attract each other to form the intervalley biexciton. We establish a semianalytical relationship between the biexciton binding energy with exciton mass and dielectric characteristics of the material and surroundings. Overall, by providing insight into the nature of diverse excitons and their correlations, our theoretical model captures the exciton interaction properties permitting an inclusive description of the structure and energy features of the intervalley biexciton in monolayer TMDs.21