Evidence of delocalized excitons in amorphous solids
arXiv:1006.5546 · doi:10.1103/PhysRevLett.105.116401
Abstract
We studied the temperature dependence of the absorption coefficient of amorphous SiO 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.