Evidence for a different type of vortex that mediates a continuous fluxoid-state transition in a mesoscopic superconducting ring

Abstract

The magnetic field response of a mesoscopic superconducting ring with an inside hole positioned off-center is studied by using the multiple-small-tunnel- junction method, by which the strengths of the superconductivity at the narrowest and the widest parts of the ring are detected separately and simultaneously. We observed continuous and reversible transitions between adjacent fluxoid states at temperatures close to the onset of superconductivity. Our findings are in agreement with numerical ones based on the Ginzburg-Landau theory, and show that in such continuous transitions, a different type of vortex nucleates at the narrowest part of the ring in the case of a low flux and at the widest part for a larger flux. The former corresponds to a one-dimensional vortex, which has been predicted theoretically for more than a decade. © 2007 The American Physical Society.