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

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.

Electrostatic Control of Nonlinear Photonic-Crystal Polaritons in a Monolayer Semiconductor

“…The corresponding exciton–exciton interaction strength is obtained as V XX1 = 1.066 μeV·μm 2 and V XX2 = 1.068 μeV·μm 2 for the groove and ridge regions in the photonic crystal unit cell, respectively. These values are in general agreement with previous results for similar samples. ,,− The nearly exact matching of the exciton–exciton interaction strength at two spatial regions is due to the minor impact of dielectric screening on the respective parameter, as discussed in refs and . We note that the saturation of blue-shifts at high fluence values is primarily due to exciton–exciton annihilation leading to a sublinear dependence of polariton density on pump fluence.…”