Imaging of super-fast dynamics and flow instabilities of superconducting vortices

L Embon,A V Silhanek,A Gurevich,E O Lachman,Y Myasoedov,G P Mikitik,Y Anahory,M V Milošević,M E Huber,Ž.L Jelić,E Zeldov

doi:10.1038/s41467-017-00089-3

Abstract

Quantized magnetic vortices driven by electric current determine key electromagnetic properties of superconductors. While the dynamic behavior of slow vortices has been thoroughly investigated, the physics of ultrafast vortices under strong currents remains largely unexplored. Here, we use a nanoscale scanning superconducting quantum interference device to image vortices penetrating into a superconducting Pb film at rates of tens of GHz and moving with velocities of up to tens of km/s, which are not only much larger than the speed of sound but also exceed the pair-breaking speed limit of superconducting condensate. These experiments reveal formation of mesoscopic vortex channels which undergo cascades of bifurcations as the current and magnetic field increase. Our numerical simulations predict metamorphosis of fast Abrikosov vortices into mixed Abrikosov-Josephson vortices at even higher velocities. This work offers an insight into the fundamental physics of dynamic vortex states of superconductors at high current densities, crucial for many applications.

Highlights

Quantized magnetic vortices driven by electric current determine key electromagnetic properties of superconductors
Jc as high as 10–20% the superconducting sotfattehebrdeeapkasirdinogwncu1–r3r.enAttdseuncshityhiJgdhatcuwrhreicnht densities J, once a vortex gets depinned from a defect, it can move with high velocity v and dissipate much power
The average vortex velocity in the stem can be estimated independently of the above analysis by assuming the distance between the moving vortices to be of the order of their mean to a 1⁄4staÀt2ioφn0a=rpy ffi3dffiBisatÁa1n=2ce1⁄4a0≅:914 μm from Fig. 2b and taking the is close highest frequency f ≅ 15 GHz from Fig. 3c

Summary

Results

The average vortex velocity in the stem can be estimated independently of the above analysis by assuming the distance between the moving vortices to be of the order of their mean to a 1⁄4staÀt2ioφn0a=rpy ffi3dffiBisatÁa1n=2ce1⁄4a0≅:914 μm from Fig. 2b (which μm) and taking the is close highest frequency f ≅ 15 GHz from Fig. 3c. The mesoscopic chains of single vortices moving along stationary channels under a dc drive and weak overheating reported here are fundamentally different from transient dendritic flux avalanches observed by magneto-optical imaging in increasing magnetic fields[41,42,43,44,45] Those macroscopic filaments of magnetic flux focused in regions overheated above Tc can propagate with velocities as high as 150 km/s in YBa2Cu3O7 films at 10 K43 or 360 km/s in YNi2B2C at 4.6 K44. The mechanisms of channeling and branching of fast vortices in our viscosity-dominated regime at J ≫ Jc are different from the disorder-driven formation of networks of slower vortices near the depinning transition observed in numerical simulations[46, 47]

Discussion

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Methods