{\it Ab--initio} finite temperature excitons

TL;DR

This paper demonstrates how lattice vibrations at finite temperatures significantly alter excitonic states, affecting energies, lifetimes, and optical properties, with successful explanation of experimental spectra in Si and BN.

Contribution

It introduces an ab-initio approach to account for finite temperature effects on excitons, moving beyond the frozen atom approximation.

Findings

Lattice vibrations renormalize exciton energies and optical strengths.

Excitons gain non-radiative lifetimes that decrease with temperature.

Temperature induces bright-dark exciton transitions.

Abstract

The coupling with the lattice vibrations is shown to drastically modify the state--of--the--art picture of the excitonic states based on a frozen atom approximation. The zero--point vibrations renormalize the bare energies and optical strengths. Excitons acquire a non--radiative lifetime that decreases with increasing temperature. The optical brightness and efficiency turn out to be strongly temperature dependent such as to induce bright to dark (and vice versa) transitions. The finite temperature experimental optical absorption spectra of bulk Si and hexagonal BN are successfully explained without using any external parameter.