THERMALLY ACTIVATED FLUX-MOTION AND QUANTUM TUNNELING OF VORTICES IN HIGH-TC SUPERCONDUCTORS

The large dissipation observed at low temperatures in epitaxial films and single crystals of YBa2Cu3O7 can be explained in terms of quantum tunneling of segments of vortices. From the magnitude of the dissipation below 1 K we find from a model based on the theories of Caldeira and Leggett, and Bardeen and Stephen that lx2hop almost-equal-to 5 x 10(-26)m3 where l is the length of the vortex segment and 2xhop is the hopping distance. This indicates that the tunneling vortex is probably a pancake of volume approximately zeta-c zeta-ab2 which is tunneling over a distance of several zeta-ab. Within the same model the fact that M(t) decays logarithmically down to 0.1 K implies that the mass of the pancake is larger than approximately 130 electron masses.