Temperature dependence of flux creep in high-T_c superconductors

The normalized decay rate R of magnetization due to thermally activated flux creep is typically given by R≃k_BT/U_c, where k_B is the Boltzmann constant, T is the absolute temperature and U_c is the effective pinning potential. Some observed data for high-T_c superconductors show that R increases with increasing T, while in other studies, R takes a peak at a certain temperature T_m below the critical temperature T_c, where T_m decreases with increasing external magnetic field. These temperature dependences of R are explained systematically on the basis of a recent theory of flux creep developed by the authors.