Indirect-exchange coupling as a basic pairing mechanism of high-temperature superconductivity: Quantitative analysis of TC( x) in electron-doped Nd 1+ xBa 2− xCu 3O y and YBa 2Cu 3O 7− x

Abstract

A quantitative analysis of critical temperatures T C( x) for the cuprate Nd 1+ x Ba 2− x Cu 3O y and the cuprate YBa 2Cu 3O 7− x is carried through on the basis of an earlier proposed, first-principle, indirect-exchange mechanism of pairing between conduction electrons (quasiparticles) mediated by closed-shell oxygen anions. We conjecture a two-component (two-phase) description for these systems, one component stable at low doping, the other at higher doping content. It is found that T C( x), including the two-plateau structure, is accurately reproduced for both systems. Doping dependence of the quasiparticle Fermi-vector length appears to determine T C( x) of the Nd-compound to a high degree of accuracy. On the other hand, in YBa 2Cu 3O 7− x the development of T C with oxygen deficiency x depends sensitively also on the density of oxygen anions as Cooper-pair mediators. A detailed analysis of these separate effects is given. In conformity with earlier applications of the same formalism, the present results strongly indicate indirect-exchange pairing as a basic mechanism in high- T C cuprate superconductivity.