  Simultaneous transport and magnetization studies in Bi2Sr2CaCu2O8 crystals at
elevated currents reveal large discrepancies, including finite resistivity at
temperatures of 40K below the magnetic irreversibility line. This resistivity,
measured at the top surface, is non-monotonic in temperature and extremely
non-linear. The vortex velocity derived from magnetization is six orders of
magnitude lower than the velocity derived from simultaneous transport
measurements. The new findings are ascribed to a shear-induced decoupling, in
which the pancake vortices flow only in the top few CuO2 planes, and are
decoupled from the pinned vortices in the rest of the crystal.
