VISCOSITY OF THE ENTANGLED-VORTEX-LIQUID PHASE

The entangled-flux-line liquid phase of high-temperature superconductors is considered. This is a phase of directed, mutually avoiding polymerlike flux lines which are strongly entangled. However, there is a finite rate constant for topological reconnection of the flux lines. The viscosity-eta of the phase is discussed using a simplified model, following that recently developed by Marchetti and Nelson [Phys. Rev. B 42, 9938 (1990)]. We find, as did these authors, a result of the form eta = eta(0)e(U/kT). However, our estimate for U is one-third of their value; the difference could be significant when the activation energy for flux-line reconnection is large.