ANISOTROPIC RESISTIVITY IN THE MIXED STATE OF CRYSTALLINE YBA2CU3O7+DELTA

An analysis of recent magnetoresistance measurements on high-quality Y -Ba-Cu-O crystals in which the angle theta of the field relative to th e c axis was varied is reported. Although the current was perpendicula r to the applied field for several of the various orientations, the da ta show evidence for comparatively small conventional flux flow; and t he data are accurately represented by a combination of phase-slip and flux-flow resistivities. We compare anisotropic expressions for phase- slip resistivity using the Ginzburg-Landau (GL) anisotropic-effective- mass formula, and the form given by Tinkham appropriate to thin films. It is shown that the resulting anistrotpic (GL) expression for the fi eld and angular-dependent phase-slip resistivity accurately describes the experimental data with the field parallel and perpendicular to the ab plane, but only approximates the angular dependence. Use of the Ti nkham expression improves the fit, suggesting that Y-Ba-Cu-O behaves a s a layered stack of ''thin film'' superconductors.