Effects of the n→s transition on the strength of superconductors

Abstract

In the transition from the normal (n) to the superconducing (s) state the creep rate of metals increases, while with deformation at constant strain rate a relaxation of the flow stress ensues. In a model developed to account for these and allied observations, phonons, emitted (n→s) or absorbed (s→n) in pairing and depairing respectively in the process of the dissolution of filamentary forms of intermediate phase retained at dislocations to temperatures somewhat below and above T _c, induce transient changes in the rates of thermal activation of the creep and relaxation. Pairing (n→s), as well as relaxation of the Cooper pair density (s→n) in the core regions of edge dislocations, is linked in the model to the occurrence of local thermal spikes. Their magnitudes are taken to be linear in the Ginzburg-Landau pair-breaking function α(T) assigned to gradients in the BCS gap-parameter at the centres of the dislocations. On introducing α/k into the equations of logarithmic creep and stress relaxation as measure of the temperature changes associated with the transients, available experimental results are well accounted for.