How do supercurrents die down when a superconductor goes normal?

The supercurrent flowing near the surface of a type I superconducting body in the presence of an external magnetic field carries kinetic energy and angular momentum. When the macroscopic body transits into the normal state and magnetic field lines start penetrating it, Faraday’s law induces electric currents opposing the change in magnetic flux, that in the aggregate carry kinetic energy and angular momentum many orders of magnitude larger than the supercurrent in the initial state. These currents die down, and their angular momentum is transferred to the body as a whole, without generation of entropy. The conventional theory of superconductivity does not explain how this happens. The alternative theory of hole superconductivity does: it requires carriers with negative effective mass. Our theory also provides an explanation for why flux is generically trapped in type I superconductors under field cooling conditions. • In the superconductor to normal transition in a magnetic field, supercurrent stops without generation of Joule heat. • The conventional theory of superconductivity has not explained how this happens. • We explain how this happens within the theory of hole superconductivity. • We explain why some flux is generically trapped in field cooling experiments with type I superconductors.