Unusually weak electron-phonon coupling in the Shockley surface state on Pd(111)

Abstract

Electron-phonon (e−ph) coupling in the ¯Γ unoccupied surface state on Pd(111) is studied using density-functional perturbation-theory calculation and two-photon photoemission measurements. Also, an ab initio GW calculation is performed to combine it with the e−ph coupling evaluation in the study of the surface-state linewidth. We show that the e−ph coupling in the surface state is unusually weak. It is smaller by a factor of 5 than that at the Fermi surface of bulk Pd. Temperature-dependent two-photon photoemission measurements confirm this result indicating an important role of interband scattering from surface to bulk states.