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 L_(a2-x)Sr_xCu_1O_4 and Y_1Ba_2Cu_3O_7 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)(d^9) orbitals; (ii) holes in the oxygen pπ bands [rather than Cu^(III)(d^8)] leading to high mobility hole conduction; and (iii) strong ferromagnetic coupling between oxygen pπ holes and adjacent Cu^(II)(d^9) 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_(1.85)Sr_(0.15)Cu_1O_4, the energy gap is in excellent agreement with experiment. For Y_1Ba_2Cu_3O_7, we find that both the CuO sheets and the CuO chains can contribute to the supercurrent.