Probing the Electronic Band Gap of Solid Hydrogen by Inelastic X-Ray Scattering up to 90GPa.

Abstract

Metallization of hydrogen as a key problem in modern physics is the pressure-induced evolution of the hydrogen electronic band from a wide-gap insulator to a closed gap metal. However, due to its remarkably high energy, the electronic band gap of insulating hydrogen has never before been directly observed under pressure. Using high-brilliance, high-energy synchrotron radiation, we developed an inelastic x-ray probe to yield the hydrogen electronic band information insitu under high pressures in a diamond-anvil cell. The dynamic structure factor of hydrogen was measured over a large energy range of 45eV. The electronic band gap was found to decrease linearly from 10.9 to 6.57eV, with an 8.6 times densification (ρ/ρ_{0}∼8.6) from zero pressure up to 90GPa.