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-x)SrₓCu₁O₄ 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 Cuᴵᴵ(d⁹) orbitals; (ii) holes in the oxygen pπ bands [rather than Cuᴵᴵᴵ(d⁸)] leading to high mobility hole conduction; and (iii) strong ferromagnetic coupling between oxygen pπ holes and adjacent Cuᴵᴵ(d⁹)melectrons. 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_(1.85)Sr_(0.15)Cu₁O₄, 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.

Group Members

William A. Goddard III

Charles and Mary Ferkel Professor