Critical Fields and Currents in Superconductors

To determine critical fields and currents in small superconducting specimens, it has long been recognized that it is necessary to take into account the effect of a change in the order parameter with field or current. This review is primarily concerned with small specimens of dimensions iess than the coherence distance, so that changes in the energy gap with position may be neglected. One may then extend the theory to arbitrary temperatures by treating the gap as a variational parameter and finding the value which makes the free energy a minimum for given fields or currents. (W.D.M.)