title: Electronic structure of crystalline 4He at high pressures.
abstract: Using inelastic x-ray scattering techniques, we have succeeded in probing the high-pressure electronic structure of helium at 300 K. Helium has the widest known valence-conduction band gap of all materials a property whose high-pressure response has been inaccessible to direct measurements. We observed a rich electron excitation spectrum, including a cutoff edge above 23 eV, a sharp exciton peak showing linear volume dependence, and a series of excitations and continuum at 26 to 45 eV. We determined the electronic dispersion along the Γ-M direction over two Brillouin zones, and provided a quantitative picture of the helium exciton beyond the simplified Wannier-Frenkel description.
authors.affiliation: Geophysical Laboratory, Carnegie Institution of Washington, Washington, DC 20015, USA.
authors.forename: Ho Kwang
authors.initials: HK
authors.lastname: Mao
authors.forename: Eric L
authors.initials: EL
authors.lastname: Shirley
authors.forename: Yang
authors.initials: Y
authors.lastname: Ding
authors.forename: Peter
authors.initials: P
authors.lastname: Eng
authors.forename: Yong Q
authors.initials: YQ
authors.lastname: Cai
authors.forename: Paul
authors.initials: P
authors.lastname: Chow
authors.forename: Yuming
authors.initials: Y
authors.lastname: Xiao
authors.forename: Jinfu
authors.initials: J
authors.lastname: Shu
authors.forename: Russell J
authors.initials: RJ
authors.lastname: Hemley
authors.forename: Chichang
authors.initials: C
authors.lastname: Kao
authors.forename: Wendy L
authors.initials: WL
authors.lastname: Mao