ANGULAR RESTRICTIONS ON THE GLASS-TRANSITION AND ON THE C-AXIS CORRELATED LIQUID-PHASE IN TWINNED YBA2CU3O7-DELTA

We have measured the angular dependence of the vortex velocity correla tion temperature T-th(H) in twinned YBa2Cu3O7-delta single crystals. T he data show that the c-axis correlated vortex liquid phase exists up to angles much larger than expected within a single vortex pinning pic ture. Despite this, the second-order solid-liquid glass transition is shown to be restricted only to external magnetic fields applied within a few degrees from the c-axis direction. (C) 1997 Elsevier Science B. V.