Excitons and trions with negative effective masses in two-dimensional semiconductors

TL;DR

This paper develops a theoretical model for excitons and trions with negative effective masses in 2D semiconductors, highlighting the importance of band non-parabolicity and providing accurate binding energy calculations.

Contribution

It introduces a novel theory for high-lying excitons and trions with negative effective mass, incorporating band non-parabolicity effects and offering simple trial wavefunctions.

Findings

Demonstrates the role of non-parabolicity in bound state formation

Provides accurate variational and numerical binding energy calculations

Connects theory with recent experimental observations

Abstract

We study theoretically fundamental Coulomb-correlated complexes: neutral and charged excitons, also known as trions, in transition metal dichalogenides monolayers. We focus on the situation where one of the electrons occupies excited, high-lying, conduction band characterized by a negative effective mass. We develop the theory of such high-lying excitons and trions with negative effective mass and demonstrate the key role of the non-parabolicity of the high-lying conduction band dispersion in formation of the bound exciton and trion states. We present simple, accurate and physically justified trial wavefunctions for calculating the binding energies of Coulomb-bound complexes and compare the results of variational calculations with those of a fully numerical approach. Within the developed model we discuss recent experimental results on observation of high-lying negative effective mass trions [K.-Q. Lin et al., Nat. Commun. 13, 6980 (2022)].