Bound vortex dipoles generated at pinning centres by Meissner current

Abstract

One of the phenomena that make superconductors unique materials is the Meissner-Ochsenfeld effect. This effect results in a state in which an applied magnetic field is expelled from the bulk of the material because of the circulation near its surface of resistance-free currents, also known as Meissner currents. Notwithstanding the intense research on the Meissner state, local fields due to the interaction of Meissner currents with pinning centres have not received much attention. Here we report that the Meissner currents, when flowing through an area containing a pinning centre, generate in its vicinity two opposite sense current half-loops producing a bound vortex–antivortex pair, which eventually may transform into a fully developed vortex–antivortex pair ultimately separated in space. The generation of such vortex dipoles by Meissner currents is not restricted to superconductors; similar topological excitations may be present in other systems with Meissner-like phases. A Meissner current is the resistance-free flow of charge induced by magnetic field in a superconductor. Here, the authors observe that Meissner currents flowing through an area containing a pinning centre generate two opposite-sense current half-loops that produce a bound vortex–antivortex pair.