Hydrodynamics of flux liquids

A hydrodynamic theory of both isotropic and hexatic flux liquids in high-${\mathit{T}}_{\mathit{c}}$ superconductors is presented. Weak microscopic pinning centers are described within the flux-flow model of Bardeen and Stephen, while strong macroscopic pinning centers set the boundary conditions for the flow. This model is relevant for understanding recent transport measurements by Worthington et al. in bulk Y-Ba-Cu-O single crystals. Flux-line entanglement leads to a large intrinsic viscosity, which increases at the isotropic-to-hexatic transition.