Electron Spectroscopy Studies of High Temperature Superconductors: Y sub (1-x) Pr sub x Ba sub 2 Cu sub 3 O sub (7-delta).

We itemize our previous work on high T sub c superconductors, and describe more fully the results of an electron spectroscopy study and impurity Anderson Hamilton analysis of the Pr 4f spectrum of Y sub (1-x) Pr sub x Ba sub 2 Cu sub 3 O sub (7- delta), a system in which superconductivity is quenched as x increases. It has been speculated that Pr has valence 4+, resulting in extra charge in the Cu-O planes, and causing T sub c -suppression. We find that the Pr valence is close to 3+ for all x but that there is entensive Pr 4f hybridization with other valence band states. The Cu valence is essentially unchanged with x. From these findings, we speculate that Pr 4f hybridization with other valence band states has enabled Pr spin fluctuations to cause the T sub c -suppression.