Photoelectron Spectroscopic Study of Zn/Cu Substituted La_1.85Sr_0.15(Cu_1−xZn_x)O_y

Abstract

A photoelectron spectroscopic study of Zn/Cu substituted polycrystalline La_1.85Sr_0.15(Cu_1−xZn_x)O_y (x=0 − 0.04) is reported. As x increases, Tc of this system decreases and superconductivity disappears for x>0.3. The reason for these occurrences is not yet clear. We have performed XPS and UPS measurements to investigate the respective core levels and the valence band, especially the density of states at the Fermi level for samples with different x’s at room temperature. The results showed that i) Zn substituted for Cu was divalent, ii) the core level binding energies of La, Sr, Cu, and O were not affected by substitution, iii) a finite DOS at the Fermi level was observed, not only for x=0 sample, but also for samples with x up to 0.04, which is not superconducting down to 4.2K. This is interesting in the sense that for a cuprate oxide, one may observe a Fermi edge with finite magnitude on samples with nearly the same carrier concentration independent of whether the sample is superconducting.