Nanoscale physics

Abrikosov vortices depinning in high-Tc 3D-anisotropic superconductor with nanoscale defect structure
Shapovalov A.P.1,2, Kasatkin A.L.1, Kalenyuk A.A.2
1 G.V. Kurdyumov Istitute of Metal Physics, NAS of Ukraine,36 Vernadsky str., 03142 Kiev, Ukraine
E-mail: shapovalovap@gmail.com
2 V. Bakul Institute for Superhard Materials, NAS of Ukraine, 2, Avtozavodskaya Str., Kiev 07074, Ukraine.

The critical current density jc value in superconductors depends on the material defect nanostructure ability to pin Abrikosov vortices and prevent them from motion which leads to the resistive state emergence and to the related electrical resistance. It is commonly assumed that the extended linear defects with radii comparable to the coherence length ξ of the superconducting state are the most effective pinning sites for vortices, ξ being about a few nanometers for the HTS materials [1]. The stability problem for the vortex pinning state is investigated by means of numerical modelling and conditions for the instability threshold are obtained as well as the critical current density jc and its dependence on the film thickness and magnetic field orientation [2]. This scenario of vortex depinning mechanism at low temperatures is strongly supported by some recent experiments on high-Tc superconductors. When the current density on the surface exceeds the critical value j0c the stationary solution for the pinned vortex string vanishes. This corresponds to the loss of stability for the pinned vortex state and starting the vortex escape from a linear defect under the Lorentz force action. When a vortex during its escape dynamics goes far enough from the defect it gets almost free from the pinning potential and travels evenly taking the stationary form of viscously moving elastic vortex string under the action of nonuniformly distributed Lorentz force. 

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