Thin Films as Superconductors Between Conventional Types I and II
Thin superconducting films are usually regarded as type-II superconductors even when they are made of a type-I materials. The reason is a strong influence of the stray magnetic fields outside the superconductive sample. While very thin films indeed reach this limit, there is a sufficiently large interval of film thicknesses in which the magnetic properties cannot be classified as either of the two conventional superconductivity types. We demonstrate that in this interval superconducting condensate and magnetic field reveal exotic spatial profiles that are very sensitive to system parameters, in particular, the temperature and applied field. Magnetic properties of such systems can be attributed to a special regime of intertype superconductivity. Its physical origin lies in the removal of infinite degeneracy of the superconducting state at the critical Bogomolnyi point. Here we demonstrate that qualitative characteristics of obtained condensate-field structures and the way they change with the temperature and applied field are independent of the choice of the in-plane boundary conditions for the order parameter and magnetic field.