Pressure effect on the superconducting transition temperature of Dy _1-xPr_xBa₂Cu₃O_7-δ

The pressure effect on the superconducting transition temperature (dT _c/dP) has been measured for Dy_1-xPr_xBa ₂Cu₃O_7-δ with x=0, 0.02, 0.05, 0.1, 0.15, 0.2, and 0.3. Although the T_c suppression by Pr is in a different fashion for Y_1-xPr_xBa₂Cu₃O _7-δ and Dy_1-xPr_xBa₂Cu ₃O_7-δ, the dT_c/dP is similar in these two systems, with respect to x. The measured dT_c/dP is positive at small x but becomes negative for x≥0.2 which is associated with the pressure effect on the normal-state resistivity (1/R)(dR/dP). The positive (1/R)(dR/dP) at x≥0.2 indicates that the number of carriers is decreasing under pressure and it supports the picture of hole localization through the hybridization of Pr-4f and O-2p bands. The mechanical pressure has a negative effect on T _c for x≥0.2, but chemical pressure has a positive effect on T _c according to the results of chemical substitution. This suggests that the large R (=rare earth element) may possibly reduce the Pr-O distance, and increase the hybridization of Pr-4f and O-2p bands.