Dissipative Fluctuation Mechanisms in Superconductors

Abstract

In the Shubnikov-Phase of a type-II superconductor, the electronic system of the bulk sample is perforated by circulating supercurrents, the well-known vortices that generate the penetrating magnetic flux quanta 0  . In a macroscopic superconductor the self-energy of such a vortex is relatively high, so that the application of an external magnetic field is necessary for the generation of the vortices. This situation changes entirely if the sample’s spatial dimensions are shrunk into the nanoscale (Fig. 1). Now thermal fluctuations with an energetic strength on the order of k T B are able to excite single-vortices in zero-magnetic field inside the superconductor (see, e.g. the famous BKT transition [1], where vortex pairs are excited). For applications of superconductivity these thermally excited vortices are troublesome because they interact electromagnetically with the bias current b I driven through the operational device. The resulting Lorentz-force leads to a dissipative vortex-motion which causes unwanted electronic noise. Therefore we focus on the fundamental quantitative understanding of these mechanisms to develop approaches that might reduce fluctuating vortices. Our aim is to enhance the performance of superconducting devices in general.