Tight-binding Hamiltonians for Sr-filled ruthenates:: Application to the gap anisotropy and Hall coefficient in Sr2RuO4

Accurate orthogonal tight-binding Hamiltonians are constructed-for ferromagnetic SrRuO3 and the layered perovskite superconductor, Sr2RuO4, by fitting to all-electron full-potential local density band structures obtained by the linearized augmented plane-wave method. These Hamiltonians allow the band structure to be computed on very fine meshes in the Brillouin zone at:low cost, and additionally have an analytic form for band velocities, while retaining the accuracy of the full-potential electronic structure calculations. This greatly facilitates calculation of transport and superconducting parameters related to the fermiology. These features are exploited to calculate the Hall coefficient and vortex lattice geometry for Sr2RuO4 with fine integration meshes. We find the upper limit for the interband order parameter anisotropy to be compatible with the observed square geometry. We also find that the sign reversal:of;the Hall coefficient can be explained in a conventional way if the bands are shifted by a few mRy so as, to match the experimental de Haas-van Alphen areas exactly, and the temperature dependence of the relaxation time is strongly dependent on the band character.