Torque creep in high-Tc superconductors

Torque relaxation measurements have been performed on single-crystal samples of Y-Ba-Cu-O and Bi-Sr-Ca-Cu-O. This technique allows us to observe the creep due to flux-line movements for in-plane circulating currents in the presence of magnetic fields either near the c axis or in the ab plane. The form of the temperature dependence of the relaxation varies considerably with the field orientation and with the material. The results, converted into voltage-gradient--current-density plots, do not show either of the alternative asymptotic behaviors predicted by the Anderson-Kim flux-creep approach or by the vortex-glass model