Measurement of critical currents of superconducting aluminum nanowires in external magnetic fields: evidence for a Weber blockade.

We have studied the critical current as a function of magnetic field in short and narrow superconducting aluminum nanowires. In the range of magnetic fields in which vortices can enter a nanowire in a single row, we find regular oscillations of the critical current as a function of magnetic field, with each oscillation corresponding to adding a single vortex to the nanowire. In this regime, the nanowires behave as quantum dots for vortices. As a function of current and magnetic field, we find diamond-shaped regions in which the resistance is zero and the number of vortices is fixed.