Electronic structure of warm dense silicon dioxide

The electronic structure of warm dense silicon dioxide has been investigated by x-ray absorption near-edge spectroscopy. An ultrafast optical laser pulse was used to isochorically heat a thin silicon dioxide sample, and measured spectra were compared with simulations generated by molecular dynamics and density functional theory. In comparison with the room temperature spectrum, two features were observed: a peak below the band gap and absorption within the band gap. This behavior was also observed in the simulations. From consideration of the calculated spectra, the peak below the gap is attributed to valence electrons that have been promoted to the conduction band, while absorption within the gap is attributed to broken Si-O bonds.