The Effect of Interband Excitations on Time-Resolved Two-Photon Photoemission via a Localized State at a Metal Surface

Abstract

The effect of interband excitations on time-resolved two-photon photoemission from an adsorbate-surface system is investigated. The system is assumed to be composed of two subbands in the bulk and a localized state of the adsorbate, which is in resonance with the upper energy subband. In the two-photon photoemission process, first, an electron in the lower energy subband is excited into the localized state by the pump photon, and subsequently excited above the vacuum level by the probe photon. The first excitation can be divided into two processes, i.e., the direct and the indirect one involving the interband excitation. The excitation probability due to the latter process reaches a maximum at a certain photon energy because of momentum conservation. A two-photon photoemission spectrum shows a peak due to the indirect process at an energy position where the initial state is fixed, as well as one due to the direct process where the intermediate state is fixed. The maximum of the cross-correlation trace of ...