INFLUENCE OF STRUCTURAL RELAXATION ON THE PARAMETERS OF A SUPERCONDUCTOR

The effect of structural defects with the internal degrees of freedom on the parameters of a superconducting material (such as critical temperature T(c), magnetic-field-penetration length lambda, and superconductor electron density N(s)) 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 lambda 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.