Photoemission study of YBa2Cu3Oy thin films under light illumination

The photocarrier injection (PCI) effect is observed at the heterojunction of YBa2Cu3Oy (YBCO) thin film and Nb-doped SrTiO3 (STO:Nb) substrate. PCI is expected as a new carrier doping method in strongly correlated systems instead of chemical substitution. We have studied the nature of PCI in YBCO/STO:Nb using X-ray photoemission spectroscopy with pulsed laser excitation. In the core-level spectra, the energy shift to higher binding energy by 0.5 eV is observed under the laser illumination with frequency of 30 Hz. The energy shift corresponds to the photovoltage, which arises in the interface. In addition, we have measured the spectra varying frequency of the laser. The energy shift obviously depends on the frequency, which is related to the lifetime of the injected photoholes. (c) 2005 Elsevier B.V. All rights reserved.