Carrier-density-related superconductivity in bismuth cuprates

We report Hall-constant ($R_H$) measurements on the Bi-Sr-Ca-Cu-O system. Two systems, 2:2:1:2 and 2:2:2:3, have been studied with a variety of heat treatments and cationic substitutions (Pb, Gd, Nd, Sm). The carrier density (n=1/${\mathrm{eR}}_H$) at 300 K as a function of $T_c$ for these polycrystalline samples show two distinct maxima—one corresponding to the low-$T_c$ (2:2:1:2) phase and the other to the high-$T_c$ (2:2:2:3) phase. The data point to compelling evidence of correlations between charge carriers and superconductivity confirming similar Hall data on Y- and La-based cuprates. A discussion of some relevant models is presented.