My question concern's the huge difference in critical fields regarding a thin superconductor(SC) which is surrounded by a magnetic field.
lets imagine the SC is a thin film in the x-y Plane: Applying a field perpendicular to that Plane destroys superconductivity way quicker than applying it parallel to the SC. Even Zeeman splitting of the DOS is observable. Why exactly do the both fields have such a different impact on the SC? Thanks
A simple way to see this is that due to the Meissner effect the magnetic field is expelled from the superconductor and field lines are deformed around the SC. Depending on the geometry of the superconductor the "density" of field lines on his surface is generally higher than the "density" of field lines away from the superconductor. This lead to an effective field at the surface higher than the one far away from the SC. For a more quantitative approach you have to study something about demagnetizing factor, while in this PDF at pages 7,8 there are some nice images showing the increasing in field line density around the surface of the superconductor.
