A Semiphenomenological Approach for Description of Quasiparticles in High Temperature Superconductors

Abstract

We present a semiphenomenological approach to calculating the quasiparticle spectra of High Temperature Superconductors (HTSC’s). It is based on a particularly efficient parametrization of the effective electron-electron interaction afforded by the Density Functional Theory for superconductors and a Tight-Binding Linearized-Mumn-Tin-Orbital scheme for solving the corresponding Kohn-Sham-Bogoliubov-de Gennes equations. We illustrate the method by investigating a number of site and orbital specific, but otherwise phenomenological models of pairing in quantitative detail. We compare our results for the anisotropy of the gap function on the Fermi surface with those deduced from photoemission experiments on single crystals of YBa₂Cu₃O₇. We also compare our predictions for the low temperature dependence of the specific heat with measurements. We investigate the doping dependence of the superconducting transition temperature, Tc. We present new evidence that the Van Hove-like scenario is an essential feature of superconductivity in these materials. Since our description of pairing is semiphenomenological, we shed new light on the physical mechanism of pairing only indirectly and conclude, provisionally, that the dominant pairing interaction operates between electrons of opposite spin, on nearest neighbour Cu sites in d _x2-y2 orbitals.