Fragmentation of Fast Josephson Vortices and Breakdown of Ordered States by Moving Topological Defects

Ahmad Sheikhzada,Alex Gurevich

doi:10.1038/srep17821

Abstract

Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Here we address the breakdown of the topologically-protected stability of such defects driven by strong external forces. We focus on Josephson vortices that appear at planar weak links of suppressed superconductivity which have attracted much attention for electronic applications, new sources of THz radiation, and low-dissipative computing. Our numerical simulations show that a rapidly moving vortex driven by a constant current becomes unstable with respect to generation of vortex-antivortex pairs caused by Cherenkov radiation. As a result, vortices and antivortices become spatially separated and accumulate continuously on the opposite sides of an expanding dissipative domain. This effect is most pronounced in thin film edge Josephson junctions at low temperatures where a single vortex can switch the whole junction into a resistive state at currents well below the Josephson critical current. Our work gives a new insight into instability of a moving topological defect which destroys global long-range order in a way that is remarkably similar to the crack propagation in solids.

Highlights

Quantized vortex lines are quintessential topological defects[1,2] which determine the behavior of superconductors and superfluids
We start with a standard theory of a Josephson vortex in a long junction described by the sine-Gordon equation for the phase difference of the order parameter θ(x, t) = φ1 − φ2 between two bulk electrodes[3,4]: θ + ηθ = θ′′ − sin θ + β
Proliferation of vortex-antivortex pairs triggered by a moving Josephson vortex can be essential for the physics and applications of weak link superconducting structures where the formation of expanding phase pile patterns can switch the entire junction into a normal state at currents well below the Josephson critical current, J > J s (0.4−0.7)J c. Such dynamic vortex instability can result in hysteretic jumps on the V-I curves which appear similar to those produced by heating effects[4,9], yet this instability is affected by neither cooling conditions nor the nonequilibrium kinetics of quasiparticles

Summary

Ordered States by Moving Topological Defects

Topological defects such as vortices, dislocations or domain walls define many important effects in superconductivity, superfluidity, magnetism, liquid crystals, and plasticity of solids. Proliferation of vortex-antivortex pairs triggered by a moving Josephson vortex can be essential for the physics and applications of weak link superconducting structures where the formation of expanding phase pile patterns can switch the entire junction into a normal state at currents well below the Josephson critical current, J > J s (0.4−0.7)J c Such dynamic vortex instability can result in hysteretic jumps on the V-I curves which appear similar to those produced by heating effects[4,9], yet this instability is affected by neither cooling conditions nor the nonequilibrium kinetics of quasiparticles. We point out a different mechanism in which a long-range order is destroyed as a single topological defect driven by a strong external force becomes unstable and triggers a cascade of expanding pairs of topological defects of opposite polarity

Methods

Findings

Additional Information