Angle resolved photoemission study of image potential states and surface states on Cu(1 1 1)

Abstract

Angle resolved non-linear photoemission induced by short laser pulses is used to investigate both the occupied surface state and the unoccupied image potential states on Cu(1 1 1). The image potential state effective mass measured at zero parallel momentum with a non-resonant photon energy between the surface state and the image potential state is significantly different from the effective mass measured at resonance in the same conditions. The surface state effective mass shows no variation with photon energy. To explain the modification of the image potential state effective mass in the non-resonant excitation, the influence of the high energy electron population in the bulk bands near the image potential state must be taken into account.