  Metallic liquid silicon at 1787K is investigated using x-ray Compton
scattering. An excellent agreement is found between the measurements and the
corresponding Car-Parrinello molecular dynamics simulations. Our results show
persistence of covalent bonding in liquid silicon and provide support for the
occurrence of theoretically predicted liquid-liquid phase transition in
supercooled liquid states. The population of covalent bond pairs in liquid
silicon is estimated to be 17% via a maximally-localized Wannier function
analysis. Compton scattering is shown to be a sensitive probe of bonding
effects in the liquid state.
