Shear-induced vortex decoupling in Bi 2 Sr 2 CaCu 2 O 8 crystals

Simultaneous transport and magnetization studies in ${\mathrm{Bi}}_{2}{\mathrm{Sr}}_{2}{\mathrm{CaCu}}_{2}{\mathrm{O}}_{8}$ crystals at elevated currents reveal large discrepancies, including finite resistivity at temperatures of 40 K below the magnetic irreversibility line. This resistivity, measured at the top surface, is nonmonotonic in temperature and extremely nonlinear. The vortex velocity derived from magnetization is six orders of magnitude lower than the velocity derived from simultaneous transport measurements. The findings are ascribed to a shear-induced decoupling, in which the pancake vortices flow only in the top few ${\mathrm{CuO}}_{2}$ planes, and are decoupled from the pinned vortices in the rest of the crystal.