Correlation between Carrier Concentration and Superconductivity in the 123-phase System

Besides the structure and oxygen content, the resistance-temperature relationship, Hall carrier concentration (nH) and midpoint temperature of superconducting transition (T_c) were measured for more than six 123-phase systems with elemental substitution. No correlation is found between the oxygen content and T_c, nor is between the orthorhombic structure and T_c. Instead, an unmonotonic relationship is jound between nH and T_c. The optimum nH for the highest T_c is about 3.8 x10²¹cm^-3. All this draws a conclusion that nH is a parameter to describe the high T_c superconductivity.