The Magnon Pairing Mechanism of Superconductivity in Cuprate Ceramics

Abstract

The magnon pairing mechanism is derived to explain the high-temperature superconductivity of both the La_2-xSr_xCu₁O₄ and Y₁Ba₂Cu₃O₇ systems. Critical features include (i) a one- or two-dimensional lattice of linear Cu-O-Cu bonds that contribute to large antiferromagnetic (superexchange) coupling of the Cu^II(d⁹) orbitals; (ii) holes in the oxygen pπ bands [rather than Cu^III(d⁸)] leading to high mobility hole conduction; and (iii) strong ferromagnetic coupling between oxygen pπ holes and adjacent Cu^II(d⁹) electrons. The ferromagnetic coupling of the conduction electrons with copper d spins induces the attractive interaction responsible for the superconductivity, leading to triplet-coupled pairs called "tripgems." The disordered Heisenberg lattice of antiferromagnetically coupled copper d spins serves a role analogous to the phonons in a conventional system. This leads to a maximum transition temperature of about 200 K. For La_1.85Sr_0.15Cu₁O₄, the energy gap is in excellent agreement with experiment. For Y₁Ba₂Cu₃O₇, we find that both the CuO sheets and the CuO chains can contribute to the supercurrent.