V. Bruyndoncx

Symmetry-induced formation of antivortices in mesoscopic superconductors.

Recent progress in nanotechnology has stimulated interest in mesoscopic superconductors as components for quantum computing and cryoelectronics. The critical parameters for superconductivity (current and field) of a mesoscopic sample are determined by the pattern of vortices in it, which in turn is controlled by the symmetry imposed by the shape of the sample (see ref. 1 and references therein). Hitherto it has been unclear what happens when the number of vortices is not consistent with the natural symmetry. Here we show that additional vortex–antivortex pairs nucleate spontaneously so as to preserve the symmetry of the sample. For example, in a square with three vortices, the spontaneously generated pair, along with the original three vortices, distribute themselves so that the four vortices sit in the four corners, with the antivortex in the centre. The measured superconducting phase boundary (of superconducting transition temperature Tc versus magnetic field strength) is in very good agreement with the calculations, giving direct experimental evidence for these symmetry-induced vortex–antivortex pairs. Vortex entry into the sample is also changed: vortices enter a square in fours, with antivortices generated to preserve the imposed vorticity. The symmetry-induced nucleation of antivortices is not restricted to superconductors, but should also apply to symmetrically confined superfluids and Bose–Einstein condensates.

Giant vortex state in perforated aluminum microsquares

We investigate the nucleation of superconductivity in a uniform perpendicular magnetic field H in aluminum microsquares containing a few (2 and 4) submicron holes (antidots). The normal/superconducting phase boundary Tc(H) of these structures shows a quite different behavior in low and high fields. In the low magnetic field regime fluxoid quantization around each antidot leads to oscillations in Tc(H), expected from the specific sample geometry, and reminiscent of the network behavior. In high magnetic fields, the Tc(H) boundaries of the perforated and a reference non-perforated microsquare re

DIMENSIONAL CROSSOVER IN A MESOSCOPIC SUPERCONDUCTING LOOP OF FINITE WIDTH

Superconducting structures with a size of the order of the superconducting coherence length

Quantization and confinement phenomena in nanostructured superconductors

ensuremath{xi}(T)

Critical temperature oscillations in magnetically coupled superconducting mesoscopic loops

have a critical temperature

Nucleation of superconductivity in a mesoscopic loop of finite width

{T}_{c},

Superconductivity in a mesoscopic double loop: effect of imperfections

oscillating as a function of the applied perpendicular magnetic field H (or flux

Confinement and quantization effects in mesoscopic superconducting structures

ensuremath{Phi}).

Vortex Confinement Phenomena in Mesoscopic Superconductors

For a thin-wire superconducting loop, the oscillations in

Connectivity and Flux Confinement Phenomena in Nanostructured Superconductors

{T}_{c}