X-Ray Photoelectron Spectroscopy Study of Oxide Superconductors La-Sr-Cu-O

The measurement of X-ray photoelectron spectroscopy（XPS）has been carried out for the superconducting oxides La_1-xSr_xCuO₃（x=0.05, 0.1, 0.3）. We found a low density of electronic state at Fermi level（N（E_F）） in each sample. A lower valence-like oxide state of Sr might exist in the sample which has a highest superconducting transition temperature （Tc）. The comparation between the results of XPS and those of resistivity measurement of Tc shows that the higher N（E_F） and the stronger asymmetry of Sr 3d^5/2 peak, the higher Tc. We believe that the low valence-like oxide state of Sr may be beneficial to high Tc.