Nonequilibrium band mapping of unoccupied bulk states below the vacuum level by two-photon photoemission.
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.
Hao
Zhaofeng
Z
Center for Integrated Science and Engineering, Columbia University, New York, New York 10027, USA.
Dadap
J I
JI
Knox
K R
KR
Yilmaz
M B
MB
Zaki
N
N
Johnson
P D
PD
Osgood
R M
RM