Pressure dependence of the superconducting transition temperature of (Y1−χPrχ)Ba2Cu3O7−δ compounds; Evidence for 4f electron hybridization

The effect of nearly hydrostatic pressure to 20 kbar on the superconducting transition temperature Tc of (Y1−χPrχ)Ba2Cu3 O7−δ compounds with 0⩽χ⩽0.5 was determined by means of low frequency ac electrical resistivity measurements. The application of pressure to this system reveals striking effects which appear to be associated with the hybridiazation between Pr 4f and valence band states. In this range of pressure P, Tc increases with P for 0⩽χ⩽0.2, exhibits a maximum at ∼6 kbar for χ=0.3, and decreases rapidly with P for χ⩾0.4, while the initial rate of increase of Tc with pressure (dTc/dP)P=0, increases with χ for 0⩽χ⩽0.3. These results suggest there is a pressure-induced electronic phase transition at ∼6 kbar foir χ=0.3 that shifts to lower values of P for higher values of χ.