Size effect on vortex states in superconducting mesoscopic aluminum disks

We report resistance measurements in superconducting Al disks whose sizes are much smaller than the superconducting coherence length of Al bulk. In the magnetic field, the disks show nonperiodic resistance peaks depending on the sample size and topology. In circular and square disks with the size of 600 nm, there is no remarkable difference in the field intervals (ΔH) of the resistance peaks. However, significant difference in ΔH are observed between circular and square disks with the size of 500 nm. These results suggest that new vortex states depending on the sample topology appear when the size is sufficiently small