First-principles interpretation of attosecond time-resolved XUV absorption spectroscopy of laser excited Silicon

The availability of ultrafast x-ray pulses both from powerful free electron laser light-sources as well as table top high-harmonic generation, has significantly enhanced the utility of core-level spectroscopies as probes for investigating dynamical processes in functional materials. Theoretical approaches to complement these time-domain experiments are therefore actively being developed. In this study we employ a combination of real-time time-dependent density functional theory (TDDFT), occupancy-constrained density functional theory and many-body perturbation theory approaches to help interpret spectral signatures observed in attosecond time-resolved core-level spectroscopic measurements on laser-excited silicon. Using non-equilibrium electron-hole densities obtained from real-time TDDFT simulations of the valence electronic structure we estimate the transient modulation of L-edge absorption in femtosecond infrared pump - attosecond XUV probe experiments. We further estimate the contribution of electron-phonon and electron-electron scattering mechanisms to the lifetime broadening observed in measured L-edge spectra using occupation-constrained density functional theory and GW calculations respectively.