Sub-picosecond dynamics in liquid Si

Abstract

We are the first group to succeed in measuring the dynamic structure factor S(Q,ω) of liquid Si close to melting using high-resolution inelastic x-ray scattering. The spectra clearly demonstrate the existence of propagating short wavelength modes in the melt with a Q–ω relation similar to those in other liquid metal systems. A specific variation of the quasi-elastic line shape with increasing Q is observed close to the structure factor maximum. This observation is related to the onset of atomic correlations on the sub-picosecond timescale in the vicinity of a metal-to-insulator transition. Such observations have been made previously only in computer simulations of metallic systems with increasing covalent character. Our data provide the first experimental evidence for these ultrashort density correlations.