Nucleation of superconductivity in a thin film with an array of holes

The results of an investigation of the surface superconductivity effect generalised for the case of a finite radius of the superconductor boundary and a multiply connected geometry of the sample are presented. It is demonstrated experimentally that in perpendicular non-zero magnetic field the critical temperature of the aluminium film with the lattice of circular holes is higher than that one of the uniform film and exhibits oscillations with magnetic field with the period approximately corresponding to one flux quantum per a hole. Another type of oscillations of the critical temperature with a smaller period (one flux per a unit cell) is observed at the same time. We discuss them in terms of the interaction between the holes. Our results can be applied for an analysis of the high-Tc materials with columnar defects because a comparison of the critical temperature versus magnetic field dependence before and after the irradiation can give some information on the properties of the amorphous tracks produced by high-energy ions.