Ultrathin, doubly connected superconducting cylinders: A link between one- and two-dimensional superconductors

In this review we summarize our work on the destructive regime, the loss of superconductivity near half-flux quanta, and present new data on the possible observation of vortex-antivortex unbinding in ultrathin, doubly connected superconducting cylinders. These cylinders were prepared by evaporating a superconducting film onto a rotating quartz filament with a diameter as small as 100 nm, which is comparable with or smaller than the zero-temperature superconducting coherence length, ξ(0). For cylinders with a relatively large diameter, bound vortex-antivortex pairs induced by thermal fluctuation and the loss of superconductivity through the unbinding of these pairs above a critical temperature are expected. However, when the diameter of the cylinder becomes smaller than ξ(0), superconductivity is lost near the half-flux quanta even in the zero-temperature limit. We argue that this unique quasi one-dimensional system provides a link between one- and two-dimensional superconductors.