SPIN-FREE QUANTUM CHEMISTRY .26. THE ISING, SMALL-BIPOLARON THEORY OF CUPRATE SUPERCONDUCTIVITY

摘要

The Ising, small-bipolaron (ISB) theory is a strong-coupling theory of cuprate superconductivity which is based on the negative-ii, Hubbard Hamiltonian. Its ground state is composed of (small) bipolarons and (small-bipolaron) holes with a vibronically induced, bipolaron-hole exchange interaction, J(BH), between them. The energy gap, Delta(0), is taken to be equal to the dissociation energy of a small bipolaron and which, since it is defined spectroscopically, is not an order parameter. The application of the Ising mean-field theory to the highly degenerate ground-state yields a second-order phase change with kT(C)/2 = J(BH) and a real order parameter, Omega(T), which is valid over the entire temperature range from zero to T-C. Near T-C, the Ising free-energy functional takes the same form as does the Landau. In the presence of an electromagnetic field, the Ising functional is a generalization of the Ginzburg-Landau functional which employs a complex order parameter and which is invariant under the electromagnetic gauge transformation. The breaking of the gauge invariance yields the London theory of superconductivity. (C) 1996 John Wiley & Sons, Inc. [References: 7]