At present it seems to be doubtful whether in the theory of supraconductivity the conception of two phases, a supraconducting and a normal phase, can describe the transformation between the two states and how far the equations which were first proposed for the pure supraconducting state in small fields remain true, when both phases are present. Especially it seems to be impossible to describe a phasetransition when an electric field is present, as probably occurs when one cools a wire carrying a constant current. However, where there is only a magnetic field the problem can be treated consistently, and the results are in agreement with experiment, and so it may be worth while to try the two-phase hypothesis, excluding equilibrium states in an electric field. The disturbance of supraconductivity by a magnetic field H T at a temperature t below the transition point has been treated thermodynamically by Gorter as a phase transition, the supraconducting phase being characterized by a zero value of the magnetic induction B

Phase-equilibrium of supraconductors in a magnetic field. (1935). Proceedings of the Royal Society of London. Series A - Mathematical and Physical Sciences, 152(877), 650–663.