Additional non equilibrium processes in the dynamic interaction between flux quanta and defects

In this work we discuss the limits of the standard analysis dealing with material defects as potential wells for flux quanta in type II superconductors. Such description, based on the thermodynamic free energy, is appropriate for quasi-static processes only, and its validity should be tested against dynamic conditions for vortices driven by a constant bias above the critical current. We briefly discuss the non equilibrium phenomena that occur during the entry and the exit of vortices from defects, comparing the characteristic times of the vortex motion with the non equilibrium characteristic time scales. Specifically, in BCS superconductors the Cooper pair recombination processes determine phonon emission and corresponding energy losses. For this reason, we underline that non equilibrium processes doubt the validity of the treatment of defects as potential wells, especially well above the critical current when vortices are driven at higher speed. © 2006 American Institute of Physics.