NONCOLLINEAR VORTEX STATES IN TWINNED YBA2CU3O7-DELTA SINGLE-CRYSTALS

The magnetic moments parallel and perpendicular to the c-axis (measure d simultaneously) have been studied as a function of direction of appl ied magnetic field H in twinned and de-twinned YBa2Cu3O7-delta single crystals. They show pronounced anomalies when the field direction appr oaches the c-axis. These allow clear identification of the angle phi(L ) at which vortices are locked into twin planes. Complete shielding of the H-ab field component (transverse Meissner effect) was observed in the locked state. For larger angles, up to phi(T), the vortices conti nue to be non-collinear with the applied field, but their direction de viates from the trapping plane. phi(L) exhibits a 1/H field-dependence , whereas phi(T) shows only weak logarithmic variations with H.