Influence of structural relaxation on the parameters of a superconductor

Abstract

The effect of structural defects with the internal degrees of freedom on the parameters of a superconducting material (such as critical temperature Tc, magnetic-field-penetration length λ, and superconductor electron density Ns) is considered using a phenomenological approach. The parameters in question are shown to exhibit local nonstationary fluctuations causing, in particular, a resistance flicker noise peak within the superconducting transition region. The magnetic noise due to fluctuations of λ has been studied as well. Another important factor is associated with local fluctuations of the critical magnetic field that lead to nonexponential magnetic-flux relaxation. It is shown that the states of the fluctuators are dependent on the state of superconducting condensate (e.g., on the presence of a supercurrent which allows some ‘‘magnetic susceptibilities’’ to be assigned to the fluctuators). Thus, in general, one deals with a coupled fluctuators-condensate system, which imposes on the condensate some glasslike features, such as slow relaxation behavior and memory effects. In particular, slow relaxation of the order parameter after a large temperature change has been shown to be expected. As for magnetic effects, a vortex acquires a polaronlike dressing by rearranged fluctuators lowering the critical field, which gives rise to a slow relaxation of the magnetic response. A specific electromagnetic absorption is also considered.

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