Theory for Coulomb scattering of trions in 2D materials

TL;DR

This paper develops a microscopic theoretical framework for Coulomb interactions between trions in 2D semiconductors, revealing their significant role in optical nonlinearity and potential for novel nonlinear phenomena.

Contribution

It introduces a comprehensive microscopic theory of trion-trion interactions, including exchange processes, and calculates their impact on optical properties in 2D materials.

Findings

Trion-trion scattering significantly affects optical nonlinearity.

The theory predicts possible attractive interactions in doped monolayers.

Calculated wavefunctions and scattering matrix elements enable future studies.

Abstract

We develop a theoretical description of Coulomb interactions between trions (charged excitons) that define a nonlinear optical response in doped two-dimensional semiconductors. First, we formulate a microscopic theory of trion-trion interactions based on composite nature of these particles, and account for all possible exchange processes. Next, we calculate numerically the trion binding energies and corresponding three-body wavefunctions using a basis set with high expressivity. Then, using the obtained wavefunctions we calculate the matrix elements of two-trion scattering, and compare the contributions coming from direct and exchange terms. Finally, we find that the considered scattering gives significant contribution to the optical nonlinearity in monolayers of transition metal dichalcogenides. In particular, this can lead to an attractive interaction in doped monolayers. Our theory opens a route for studying nonlinear properties of trion-polaritons inaccessible before.