ABSTRACT
The London equations do not give a completely satisfactory macroscopic picture of all superconducting phenomena in a magnetic field, because they regard the specimen as being either entirely superconducting or entirely normal. Thus they cannot come to grips with the intermediate state, where the specimen has both normal and superconducting regions coexisting simultaneously, owing to the energetic favorability of the formation of normal-superconducting boundary layers. Recent detailed study of the microscopic theory has served not only to confirm the essential correctness of the Ginzburg–Landau (GL) equations in their original context, but to extend their domain of validity to regimes not previously considered possible; earlier work using the equations thus has taken on a wider meaning and an increased relevancy. The goal of deriving a time-dependent GL theory really means establishing a simple differential equation in time and space variables for the order parameter.
