Statistical mechanics of the local-pair superconductor: phase diagrams and specific heats

Abstract

The quantum-lattice-gas model, originally introduced by Matsubara and Matsuda to describe the superfluid properties of 4He, relates the hamiltonian of a system of hard-core bosons hopping on a lattice with nearest-neighbour transfer integral t and interaction v, to that of a spin S = 1 2 , uniaxially anisotropic Heisenberg antiferromagnet in a magnetic field. Interest in the charged-boson version of this model has recently been revived since it describes the superconductivity (superfluidity) of local pairs of carriers (negative-U centers). Here we investigate its application to the phase diagrams of T c versus carrier density, and the ordering anomalies in the specific heat of the superconducting oxides.