Vortex flow and transverse flux screening at the Bose glass transition

We study the vortex phase diagram in untwinned YBCO crystals with colunmar defects. These randomly distributed defects are expected to induce a "Bose glass" phase of localized vortices exhibiting a vanishing resistance and Me issner effect for magnetic fields H-perpendicular to transverse to the colu mns. We directly observe the transverse Meissner effect using a Hall probe array. As predicted, the Meissner state breaks down at temperatures T-x tha t decrease linearly as H-perpendicular to increases. However, T-s lies far below the conventional melting temperature T-m determined by a vanishing re sistivity, suggesting a regime where vortices are effectively localized eve n when rotated off the columnar defects.