Vortex liquids in high-temperature superconductors (invited)

Recent work on the hydrodynamic theory of vortex liquids in high-T _c superconductors is reviewed. Weak microscopic pinning centers are described within the flux-flow model of Bardeen and Stephen, while strong macroscopic pins set the boundary conditions for the flow. Entanglement and intervortex interactions can yield an exceptionally large intrinsic viscosity for the vortex liquid. This large viscosity allows the effect of a few strong pins to propagate over large distances and choke off the flow. As a new and experimentally relevant example of spatially inhomogeneous pinning on macroscopic scales, we consider the response of the flux liquid to an alternating current within a simple model that incorporates viscoelastic properties of the vortex liquid.