$ extit{Ab initio}$ evidence for nonthermal characteristics in ultrafast laser melting

摘要

Laser melting of semiconductors has been observed for almost 40 years;surprisingly, it is not well understood where most theoretical simulations showa laser-induced thermal process. $\textit{Ab initio}$ nonadiabatic simulationsbased on real-time time-dependent density functional theory reveal intrinsicnonthermal melting of silicon, at a temperature far below the thermal meltingtemperature of 1680 K. Both excitation threshold and time evolution ofdiffraction intensity agree well with experiment. Nonthermal melting isattributed to excitation-induced drastic changes in bonding electron density,and the subsequent decrease in the melting barrier, rather than lattice heatingas previously assumed in the two-temperature models.