General features of quantum creep in high-Tc superconductors

Measurements of the relaxation rate Q(T) of superconducting currents have been performed on a carefully selected set of dirty and clean high-T-c;. superconductors for temperatures T down to 100 mK and magnetic fields up to 7 T. The extrapolated relaxation rates Q(0) for the dirty compounds indicate that the viscosity experienced by a tunneling vortex segment is grossly underestimated by the standard Bardeen-Stephen theory. For the clean compounds a universal value Q(0) congruent to 0.022 is found at 1 T, implying that the number of superconducting charge carriers involved in the tunneling of a vortex segment is congruent to 14.