Superflow in d-wave superconductors

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