THERMALLY ACTIVATED FLUX MOTION NEAR THE ABSOLUTE-ZERO

Recent experimental studies of the magnetization M(t) relaxation of high-T(c) superconductors lead to the conclusion that a sizeable relaxation occurs down to 100 mK and that both dM/dln t and dln M/dln t do not extrapolate linearly to zero as expected from a standard thermally activated flux motion model (TAFM). We show here that for a wide class of pinning potentials the time derivatives of the magnetization vary as T1/n with n greater-than-or-equal-to 3/2 at low temperatures.