Two-photon photoemission spectroscopy

Abstract

Unoccupied electronic states of optimally doped high-temperature superconductor Bi2212 have been measured by two-photon photoemission (2PPE). The results demonstrate the capability of 2PPE spectroscopy to probe unoccupied states and the electron dynamics of metal oxides. The lateral resolution of 2PPE spectroscopy was improved to 0.6 Ｌm by focusing the laser light. Surface images based on the unoccupied image potential state of Cu(111) formed on a polycrystalline copper plate were successfully obtained.