Photoemission investigation of the high temperature superconductors La2−x Sr x CuO4

Photoemission spectra of the La_2–xSr_xCuO₄ system which recently has been demonstrated of being capable to produce high temperature (T_c>35 K) superconducting compounds are reported. The photoemission spectra of the basic system (La₂CuO₄) and of samples which contain up to 20% Sr are not significantly different. The density of states at the Fermi energy is small (smaller than that of metallic Cu) and the samples show a possible small shift of the Cu 2p lines towards the trivalent position with increasing tendency to superconductivity. From the Sr 3d spectra a considerable amount of oxygen defects coordinated to the Sr ions is estimated.