Decay of metastable states of high Tc and conventional “low Tc” superconductors

Abstract

The time decay of the zero field cooled and remanent magnetization has been measured in several high-temperature superconductors, Ti 50V 50 and V 3Si single crystals. It is shown that the dynamics of vortices in both types of superconductors can be described on a very coherent way by using the mean relaxation time τ defined at a constant level of mixed state. The mean energy barrier E which is associated with this relaxation time is found to be proportional to the reciprocal magnetic field. The temperature variation of the penetration and exclusion rate of vortices obeys an Arrhenius type equation with an effective temperature T ∗=( θ 2) coth( θ 2T ) . Here, θ is a characteristic temperature closely related to the crossover from thermal process and to quantum tunneling of vortices. At still lower temperatures, large flux jumps appear in the magnetization curves. Temperature changes have been observed corresponding to these jumps in V 3Si crystals.