Flux pinning and creep in high-$T_c$ superconductors

We report here calculations of intrinsic (lattice) as well as point defect induced pinning, using a realistic Ginzburg-Landau theory. The former mechanism is shown to be effective for a vortex line parallel to the Cu-O planes, and the latter for a vortex line perpendicular to them. We show that local kink-antikink pairs on otherwise straight vortex lines can be made metastable by pinning. We argue that these metastable defects cause flux noise and dissipative flux creep in the linear regime at low temperature and magnetic fields. These defects are shown to have the observed size and orientation dependence of the activation energy, and to rationalize a variety of properties of transport and magnetic behaviour