Nonlinear current dependence of potential barrier for flux creep in superconducting La-Sr-Cu-O single crystal

The potential barrier for flux bundles, U, was estimated from the observed relaxation of the magnetization, M, with time, t, in a superconducting La-Sr-Cu-O single crystal. It is shown that U depends on the current density, J, and the temperature, T, as U(J, T)=U0[(J0/J)α-1]. The present result is different from the relationship of U ∝ ln (J0/J) observed in Y-Ba-Cu-O films, and is similar to the one predicted by the collective theory. It is also pointed out that the observed increase of the effective pinning potential, Uc*=kBT(-&part ln M/&part ln t)-1, with increasing T does not result from the T dependence of U0, but is only an apparent anomaly originating from above nonlinear U-J characteristics.