VORTEX DYNAMICS IN OXYGEN-DEFICIENT SINGLE-CRYSTALS OF YBA2CU3O7-DELTA

In YBa2Cu3O7-delta (YBCO), oxygen deficiencies in the CuO chains chang e the coupling between the charge carriers in adjacent superconducting CuO2 planes and thereby the electrical anisotropy, gamma=(m(c)/m(ab)) (1/2). Such crystals therefore provide a simple test system for system atic studies of the influence of anisotropy on vortex dynamics. We hav e studied the vortex glass transition of YBCO single crystals with del ta in the range of 0.07 to 0.27, corresponding to gamma between 9 and 18, for magnetic fields 0<B<12 T, along the c-axis. Fits of the glass transition lines to B proportional to (1-T/T-c)(alpha) show large devi ations for a combination of high anisotropy and high magnetic fields.