Significance of nonorthogonality in tight-binding models. II. The possibility of high-Tc superconductivity in intercalation compounds.

Abstract

Using the L\"owdin transformation from nonorthogonal atomic orbitals to orthogonal Wannier orbitals for the tight-binding model with many-body interactions, we derive the t-J model for graphite. We demonstrate the significance of nonorthogonality on the parameters t and J. We obtain a mean-field phase diagram for the critical temperature ${\mathit{T}}_{\mathit{c}}$ versus doping fraction using an auxiliary slave-boson method. We compare the stabilization of the superconducting phase transition via a weak interlayer coupling with a Kosterlitz-Thouless two-dimensional dilute Bose gas condensation. It is concluded that graphite intercalation compounds form a testing ground for the t-J model of high-${\mathit{T}}_{\mathit{c}}$ superconductivity independent of the cuprates.