Quasiparticles in d-wave superconductors within density functional theory

Abstract

We present a semiphenomenological approach to calculating thequasiparticle spectra of high-temperature superconductors. It isbased on a particularly efficient parametrization of the effectiveelectron-electron interaction afforded by the density functionaltheory for superconductors and atight-binding linearized-muffin-tin-orbital scheme for solving thecorresponding Kohn-Sham-Bogoliubov-de Gennes equations. We applythis methodology to YBa2Cu3O7-δ (YBCO) andillustrate its potential by investigating a number of site- andorbital-specific, but otherwise phenomenological, models of pairingin quantitative detail. We compare our results for the anisotropyof the gap function on the Fermi surface with those deduced fromphotoemission experiments on single crystals of YBCO. Also, the low-temperature specific heat and penetration depth are calculated andcompared with measurements. We investigate the doping dependence ofthe superconducting gap, transition temperature, Tc, andpenetration depth. We present new evidence that the Van Hove-likescenario is an essential feature of superconductivity in the cupratesuperconductors. Since our description of pairing isphenomenological, we shed new light on the physical mechanism ofpairing only indirectly and conclude, provisionally, that thedominant pairing interaction operates between electrons of oppositespins, on nearest-neighbour Cu sites in dx2-y2 orbitals.