High-pressure study on high-T_c (ZnPc) Bi-2223 oxides

We have measured the pressure effect on the superconducting transition temperature T_c and the normal-state resistivity R for the high-T_c Bi-2223 oxides intercalated with zinc-phthalocyanine (ZnPc). At ambient pressure, T_c is degraded from 110 K to 90 K with the intercalation of 0.01 ZnPc per unit cell, and T changes its temperature dependence from metallic to semiconducting-like behavior, suggesting that the intercalation affects the electronic structure of the CuO₂ plane significantly. We have obtained dT_c/dP=1.9±0.3, 1.7±0.4 and 1.8±0.3 K/GPa for samples with T_c=110, 100 and 90 K, respectively. On the other hand, the normalized pressure effect on the normal-state resistivity dln R/dP is rather different for these three samples, changing from 2%/GPa to -20%/GPa. We have tentatively ascribed the nearly constant value of dT_c/dP (≈2 K/GPa) to the pressure effect on the hopping integrals of the conducting holes, and the large variation in dln R/dP to the enhanced compressibility along the c-axis.