On the pressure dependence of Tc of the Y 1- xPr xBa 2Cu 3O 7-δsystem

Abstract

It is shown that the crossover which occurs with increasing x near x ≃ 0.2 in the pressure dependence of the superconducting critical temperature T c from positive to large negative values for the Y 1- x Pr x Cu 3O 7-δ (δ ≃ 0.05) system can be be accounted for using a simple phenomenological model, generalized to include pressure. The model was developed to describe the dependence of T c on the concentrations of Pr ( x) and Ca ( y) and Ca ( y) in the Y 1- x- y Pr x Ba 2Cu 3O 7-gd system and incorporates (1) the counteracting effects of the generation and annihilation of holes in the conducting CuO 2 planes by Ca 2+ and Pr n+ ions (where + n is the Pr valence), respectively, and (2) the deparing of superconducting electrons via exchange scattering of the mobile holes in the CuO 2 planes by the Pr magnetic moments. New measurements of T c(P) on higher quality Y 1- x Pr x Ba 2Cu 3O 7-δ specimens are presented and analyzed in terms of the phenomenological model. The increase in the magnitude of the normal state electrical resistivity with pressure observed in an Y 0.5Pr 0.5Cu 3O 7-δ specimen is consistent with the decrease in the mobile hole concentrations with pressure inferred from the model.