Nucleation of vortices inside open and blind microholes.

The critical field of a thin superconducting film with a blind circular hole is found theoretically. It is shown that the value of the critical field is sensitive to the bottom thickness, but the orbital momentum, i.e., the number of vortices which nucleate inside the hole, is not sensitive. A simple boundary condition for a steplike thin film is derived and used for comparative numerical analysis of the superconductivity nucleation in a microdisk and near the hole. By increasing the thickness of the bottom of a blind hole one can transform the hole into a disk of the same radius which rests on top of the film. We show that such transformation leads to a jump in the number of vortices which nucleate at the critical magnetic field inside the perimeter of the hole ~the disk!. We report also the results of the Bitter decoration experiments of a thin superconducting film with a lattice of open or blind holes. It is found ~in accordance with the calculation! that the bottom thickness has only a weak influence on the number of vortices captured by a hole during the cooling of the sample at a constant perpendicular magnetic field. All the experimental results are explained under the assumption that the vortices nucleated inside a hole rest inside during the cooling process and no additional vortices enter the hole.