Evidence of delocalized excitons in amorphous solids

TL;DR

This study provides evidence that excitons in amorphous SiO$_2$ are delocalized despite structural disorder, by analyzing temperature-dependent absorption spectra and demonstrating excitonic resonance behavior.

Contribution

It presents the first clear evidence of delocalized excitons in amorphous solids through detailed spectral analysis and temperature dependence.

Findings

Excitonic resonance at 10.4 eV shifts with temperature.

Excitons are coupled to an 83 meV phonon mode.

Delocalized excitons exist despite amorphous disorder.

Abstract

We studied the temperature dependence of the absorption coefficient of amorphous SiO$_2$ in the range from 8 to 17.5~eV obtained by Kramers-Kronig dispersion analysis of reflectivity spectra. We demonstrate the main excitonic resonance at 10.4~eV to feature a close Lorentzian shape red-shifting with increasing temperature. This provides a strong evidence of excitons being delocalized notwithstanding the structural disorder intrinsic to the amorphous system. Excitons turn out to be coupled to an average phonon mode of 83~meV energy.