title: Nonequilibrium band mapping of unoccupied bulk states below the vacuum level by two-photon photoemission.
abstract: We demonstrate angle-resolved, tunable, two-photon photoemission (2PPE) to map a bulk unoccupied band, viz. the Cu sp band 0 to 1 eV below the vacuum level, in the vicinity of the L point. This short-lived bulk band is seen due to the strong optical pump rate, and the observed transition energies and their dispersion with photon energy ℏω, are in excellent agreement with tight-binding band-structure calculations. The variation of the final-state energy with ℏω has a measured slope of ∼1.64 in contrast to values of 1 or 2 observed for 2PPE from two-dimensional states. This unique variation illustrates the significant role of the perpendicular momentum ℏk_{⊥} in 2PPE.
authors.affiliation: Center for Integrated Science and Engineering, Columbia University, New York, New York 10027, USA.
authors.forename: Zhaofeng
authors.initials: Z
authors.lastname: Hao
authors.forename: J I
authors.initials: JI
authors.lastname: Dadap
authors.forename: K R
authors.initials: KR
authors.lastname: Knox
authors.forename: M B
authors.initials: MB
authors.lastname: Yilmaz
authors.forename: N
authors.initials: N
authors.lastname: Zaki
authors.forename: P D
authors.initials: PD
authors.lastname: Johnson
authors.forename: R M
authors.initials: RM
authors.lastname: Osgood