X-ray Absorption Near-Edge Spectroscopy (XANES) of Warm Dense Silicon Dioxide

The electronic structure of warm dense silicon dioxide has been investigated by X-ray Absorption Near-Edge Spectroscopy (XANES). An ultrafast optical laser pulse isochorically heats a thin sample. The measured XANES spectra are compared with simulations generated by molecular dynamics and density functional theory. Three new features are observed: a peak below the band gap, absorption within the band gap and a broadening of the absorption edge. From comparison with the calculations, the peak below the band gap provides a measurement of the electron temperature while the spectral features above the O K-edge constrain the ion temperature. Further, the absorption within the gap presents evidence for broken Si-O bonds. The XANES is interpreted as that of a non-equilibrium liquid.