Fluxoid solitons in superconducting tapered tubes and bottlenecks

TL;DR

This paper introduces fluxoid solitons in superconducting tapered tubes with bottlenecks, revealing their topological nature, properties, and arrangements, expanding understanding of vortex-like excitations in superconductors.

Contribution

It presents the discovery and characterization of fluxoid solitons as a new topological vortex type in superconducting tubes with variable radius, using self-consistent quasiclassical theory.

Findings

Fluxoid solitons are topologically protected solutions in superconducting bottlenecks.

Multiple fluxoid solitons can form complex arrangements due to mutual repulsion.

Fluxoid solitons are loosely related to Pearl vortices and fluxons.

Abstract

A thin-walled tubular superconductor develops a quantized fluxoid in the presence of an axial magnetic field. The fluxoid corresponds to the number of phase windings of the superconducting order parameter and is topological in nature. When the tube has a radius variation along the axial direction, forming a bottleneck structure between sections with different radius, a fluxoid mismatch can appear depending on the applied magnetic field. The bottleneck then becomes a topological boundary and is host to topologically protected solutions for the order parameter, dubbed fluxoid solitons, that are free to move around bottlenecks with cylindrical symmetry. Fluxoid solitons are a new type of vortex with non-quantized flux, loosely related to Pearl vortices in thin superconducting films and fluxons in Corbino Josephson junctions. We characterize their properties as a function of system parameters using the self-consistent quasiclassical theory of diffusive superconductors. We consider both short bottleneck structures and long tapered tubes, where multiple trapped fluxoid solitons adopt elaborate arrangements dictated by their mutual repulsion.