Optical Absorption by Dirac Excitons in Single-Layer Transition-Metal Dichalcogenides

TL;DR

This paper presents an analytical model explaining the unique nonhydrogenic exciton spectra observed in 2D transition-metal dichalcogenides by incorporating pseudospin-related angular momentum.

Contribution

It introduces a novel exciton Hamiltonian that explicitly includes pseudospin angular momentum, crucial for understanding exciton spectra in 2D honeycomb materials.

Findings

Qualitative explanation of nonhydrogenic exciton spectra

Inclusion of pseudospin angular momentum is essential

Model aligns with recent experimental observations

Abstract

We develop an analytically solvable model able to qualitatively explain nonhydrogenic exciton spectra observed recently in two-dimensional (2d) semiconducting transition metal dichalcogenides. Our exciton Hamiltonian explicitly includes additional angular momentum associated with the pseudospin degree of freedom unavoidable in 2d semiconducting materials with honeycomb structure. We claim that this is the key ingredient for understanding the nonhydrogenic exciton spectra that was missing so far.