Superflow in d-wave superconductors

Superflow in a phenomenological tight-binding model for the superconducting state of some high-temperature superconductors is discussed thoroughly. Th e formalism used is explicitly gauge invariant and currents are computed ex actly within the BCS theory, going therefore beyond linear response theory. The dependence of gap functions, current density, critical currents and fr ee energy as a function of the superfluid velocity for different angles and doping concentrations is investigated. Different sources of anisotropy, li ke the dispersion relation of the model, the internal symmetry of the order parameter, and orthorhombic distortions of the lattice are also studied. ( C) 1999 Academic Press.