Fluxons in high-impedance long Josephson junctions

TL;DR

This paper demonstrates experimentally that high-impedance long Josephson junctions with high kinetic inductance superconductors can significantly slow fluxons and increase impedance, opening new possibilities for superconducting electronics.

Contribution

The study introduces a novel type of long Josephson junction with high kinetic inductance electrodes that reduces fluxon velocity and enhances impedance, unlike conventional junctions.

Findings

Swihart velocity reduced by about tenfold

Characteristic impedance increased by an order of magnitude

Fluxons carry significantly less magnetic flux than the flux quantum

Abstract

The dynamics of fluxons in long Josephson junctions is a well-known example of soliton physics and allows for studying highly nonlinear relativistic electrodynamics on a microscopic scale. Such fluxons are supercurrent vortices that can be accelerated by a bias current up to the Swihart velocity, which is the characteristic velocity of electromagnetic waves in the junction. We experimentally demonstrate slowing down relativistic fluxons in Josephson junctions whose bulk superconducting electrodes are replaced by thin films of a high kinetic inductance superconductor. Here, the amount of magnetic flux carried by each supercurrent vortex is significantly smaller than the magnetic flux quantum $ \Phi_0 $. Our data show that the Swihart velocity is reduced by about one order of magnitude compared to conventional long Josephson junctions. At the same time, the characteristic impedance is increased by an order of magnitude, which makes these junctions suitable for a variety of applications in superconducting electronics.