Correlated two-particle excitation mechanism for high-T_c superconductors

Abstract

Taking cognizance of recent experimental work showing the existence of the species O^2-₂ and concomitantly of Cu^l+ in the high T_c superconductors (La_1·8Sr_0·2CuO₄ and YBa₂Cu₃O_7-δ ) a theoretical mechanism for the pairing of quasiparticles is suggested. This mechanism involves virtual two particle excitations to states of Cu^l+(O^2-₂) species and is reminiscent of correlation superexchange in some antiferromagnets. This electronic mechanism leads to anisotropic s-wave pairing of quasiparticles. The expression for the transition temperature is a combination of phonoc and electronic mechanisms, the latter depending on the concentration of the species in question, (concomitantly related to hole concentration). The calculated trend of T_c as a function of species (hole) concentration falls within the available experimental data.