Orbital symmetry and the optical response of single-layer monochalcogenides

TL;DR

This study uses first-principle calculations to analyze how the optical absorption spectra of single-layer GaSe and GaTe are affected by exciton states and light polarization, revealing tunable optical properties linked to symmetry.

Contribution

It demonstrates the polarization-dependent optical response of single-layer GaSe and GaTe due to symmetry, providing insights into exciton coupling mechanisms using GW-BSE calculations.

Findings

Exciton peaks are polarization-selective due to symmetry.

Absorption peaks vary with light polarization and incident angle.

Overall absorbance decreases at large incident angles for p-polarized light.

Abstract

The absorption spectra of single-layer GaSe and GaTe in the hexagonal phase feature exciton peaks with distinct polarization selectivity. We investigate these distinct features from first-principle calculations using the GW-BSE formalisms. We show that the brightness of the exciton absorption peaks is tunable with the polarization of the light. Due to the symmetry of the bands under z-axis mirror symmetry, the bound exciton states selectively couple to either in-plane or out-of-plane polarization of the light. In particular, for a p-polarized light absorption experiment, the absorption peaks of the s-like excitons emerge at large angle of incidence, while the overall absorbance reduces over the rest of the spectrum.