Specific-heat anomaly near Tc of the (Bi,Pb)-Sr-Ca-Cu-O superconductor (Tc=107 K)

Specific-heat measurements of the 107-K phase of the (Bi,Pb)-Sr-Ca-Cu-O system were made in the temperature range 80250 K by an ac calorimetry method. A finite specific-heat jump at Tc (Cp/Tc=16 mJ mol-1 K-2) was first detected, from which the electronic specific-heat coefficient was calculated through the BCS relationship, i.e., 11 mJ mol-1 K-2, corresponding to the density of states N(0)=0.8 states eV-1 (Cu atom)-1 spin-1. This N(0) value was rather smaller than that of (La1-xMx)2CuO4 (M=1/rSr,Ca) or Ba2YCu3O7. This is in contrast with the usually observed positive correlation between Tc and N(0) among the conventional metallic superconductors. A broadened transition width and the sharpened peak at Tc observed in the CpT curve was attributed to the two-dimensional superconducting fluctuation effect with coherence length (0)=13 i/rA in the plane.