ENHANCEMENT EFFECT DUE TO HOP-ON AND HOP-OFF INTERACTION BETWEEN COOPER PAIR AND BIPOLARON ON THE CHARACTERISTICS OF THE HIGH-Tc CERAMIC SUPERCONDUCTOR

Abstract

Enhancement in the critical temperature of high-Tc ceramic superconductors has been studied based on the bipolaronic theory which involves the hop-on and hop-off interaction between the Cooper pair and the bipolaron. As a consequence, the BCS energy gap is broadened to a certain extent which is determined by the interaction between the Cooper pair and the bipolaron. The effective superconducting energy gap for the ceramics consists of two parts: the traditional BCS energy gap of the ceramic and the gap broadening contributed by the hop-on and hop-off process. The critical temperature has been formulated from the effective BCS energy gap, and expressed in terms of the electronegativity difference Δχ. Results of our calculation on the critical temperature for MBCO-type, T(n) BCCO , and HBCCO match with the experimental data excellently. For a certain series of ceramic superconductors, the variation of Tc against Δχ traces out a curve having a high enough maximum value, in general.