Quasimomentum-Space Image for Ultrafast Melting of Silicon.

By exciting electron-hole pairs that survive for picoseconds strong femtosecond lasers may transiently influence the bonding properties of semiconductors, causing structure changes, in particular, ultrafast melting. In order to determine the energy flow during this process in silicon we performed ab initio molecular dynamics simulations and an analysis in quasimomentum space. We found that energy flows very differently as a function of increasing excitation density, namely, mainly through long wavelength, L-point, or X-point lattice vibrations, respectively.