Mesoscopic Superconducting Disc with Short-Range Columnar Defects

The use of submicron Hall probe technique in the ballistic regime for studying individual submicron superconducting samples smaller than the probe size allowed to establish a link between the detected signal and the sample magnetization. These experiments show that the sample undergoes a sequence of phase transitions of the first kind, which manifest themselves as mesoscopic jumps of the magnetization curve [2]. The jumps are due to penetrations of additional vortices inside the superconductor as the applied magnetic field increases. The relation of the magnetization jumps to the penetration of new vortices into the disc has been demonstrated in a series of theoretical works. It was shown that S-N transition in mesoscopic disc could be of first or second order. The conditions for multi-vortex states or a giant vortex state formation were analyzed. It occurred that above the upper critical field for an infinite sample the vortices always form a giant vortex located at the disc center [6]. In the present report we study the magnetic properties of a mesoscopic superconducting disc with disordered short-range columnar defects. We show that the defects help the penetration of vortices into the sample, thereby decrease the sample magnetization and reduce its upper critical field. Even weak defects split a giant vortex state into a number of vortices with smaller topological charges. In a disc with a sufficient number of strong enough defects vortices are always placed onto defects. The presence of defects lead to the appearance of additional magnetization jumps related to the redistribution of vortices which are already present on the defects and not to tile penetration of new vortices