Stability of bubble-like fluxons in disk-shaped Josephson junctions in the presence of a coaxial dipole current

Abstract

We investigate analytically and numerically the stability of bubble-like fluxons in disk-shaped heterogeneous Josephson junctions. Using ring solitons as a model of bubble fluxons in the twodimensional sine-Gordon equation, we show that the insertion of coaxial dipole currents prevents their collapse. We characterize the onset of instability by introducing a single parameter that couples the radius of the bubble fluxon with the properties of the injected current. For different combination of parameters, we report the formation of stable oscillating bubbles, the emergence of internal modes, and bubble breakup due to internal mode instability. We show that the critical germ depends on the ratio between its radius and the steepness of the wall separating the different phases in the system. If the steepness of the wall is increased (decreased), the critical radius decreases (increases). Our theoretical findings are in good agreement with numerical simulations.We discuss applications in quantum information technologies.

Thermal flux-flow regime in long Josephson tunnel junctions

“…In a long Josephson tunnel junction, i.e., a junction in which one dimension is longer than the Josephson penetration length [61], the externally applied magnetic field can penetrate the junction in the form of fluxons. This kind of excitations can be controlled and handled in different ways, for instance they can be moved by a bias current, or created by a magnetic field or a dissipative hotspot [32,33], pinned by inhomogeneities [34,35], and also manipulated through shape engineering [36][37][38][39]. Additionally, it was recently understood that solitons can induce thermal effects in a temperature-biased junction, so that applications as thermal router [1,40] and heat oscillator [41] have been suggested.…”