Polarization-dependent X-ray absorption spectroscopy of La2CuO4Fx thin films using synchrotron radiation

High-resolution polarization-dependent O K-edge x-ray absorption spectra fo r c-axis oriented La2CuO4Fx thin films were investigated. In the O 1s absor ption edge of La2CuO4Fx, the prepeak at 528.7 eV is assigned to transitions into O 2p(xy) hole states located in the CuO2 planes. Fluoride ions presen t in La2CuO4Fx induce hole states in the CuO2 planes near the Fermi level, which in turn play an important role in enhancing superconductivity for thi s compound, as compared to parent La2CuO4. In La2CuO4Fx, fluoride ions are regarded as an electronic dopant to induce superconductivity.