Magnetic relaxation in hard type-II superconductors

Magnetic relaxation in a type-II superconductor is simulated for a range of temperatures T in a simple model of the 2D Josephson junction array (JJA) with finite screening. The high-T phase, that is characterised by a single time scale tau(alpha), crosses over to an intermediate phase at a lower tem perature T-cr wherein a second time scale tau(beta) much less than tau(alph a), emerges. The relaxation in the time window set bg tau(beta) follows a p ower law which is attributed to self-organization of the magnetic fins duri ng relaxation. Consequently, for T < T-cr, a transition from super-critical (current density J > J(c)) to sub-critical (J < J(c)) slate separated by a n intermediate state with frozen dynamics is observed. Both tau(alpha) and tau(beta) diverge at T-sc < T-cr, marking the transition into a state with true persistent current.