Vortex Pinning and Dynamics in HTS films: Role of Extended Linear Defects
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Vortex Pinning and Dynamics in HTS films: Role of Extended Linear Defects Alexander L. Kasatkin, Constantin G. Tretiatchenko, Volodymyr M. Pan Institute of Metal Physics, National Academy of Sciences of Ukraine, 36 Vernadsky Blvd., 03142 Kiev, Ukraine ABSTRACT The model of single vortex escape from extended linear defect and subsequent vortex dynamics under the Lorentz force action in a rather thick (d > 2λ) 3D anisotropic superconductor is developed. We consider the case of parallel c-oriented linear defects as well as the case of equidistant linear row of such kind of defects, which represents the dislocation model of lowangle [001] tilt grain boundary in HTS films and bicrystals. The suggested model based on the classical mechanics approach allows to describe behavior of an elastic vortex string in the potential well of linear defect and under the action of Lorentz force on its end within the Meissner current carrying layer and to determine the depinning critical current density at low magnetic fields and temperatures. INTRODUCTION Extended linear defects in HTS superconductors with a diameter of few nanometers comparable with the coherence length are known to be strong pinning sites for Abrikosov vortices providing high critical current values. In HTS single crystals artificial columnar defects produced by heavy-ion irradiation can significantly effect different properties of superconductor and substantially improve its electrodynamic characteristics in the mixed state, e.g., increase the critical current density, enhance the irreversibility field Hirr(T) and melting temperature of vortex lattice Tm(H) [1], etc. The role of extended linear defects in HTS epitaxial films is usually played by as-grown c-oriented edge and screw dislocations emerging during the film growth [2, 3]. Usually low-angle grain boundaries (LAB) in HTS bicrystals and epitaxial films and are formed as chains of c-oriented edge dislocations, which are ordered in a 2D network over the film plane [4, 5]. There is an additional type of linear defects in HTS films containing nanoparticles of an admixture phase (BZO, Y-211, etc.) – nanorods formed due to self-organization of added nanoparticles [6, 7]. In the present work the model of single vortex escape from a linear defect under the influence of inhomogeneously distributed Lorentz force is developed both for the cases of randomly distributed c-oriented linear defects and those aligned in an equidistant onedimensional row (model of [001] tilt LAB in HTS bicrystal), low temperatures and not too high magnetic fields. We have calculated the critical current density jc, at which the instability, leading to vortex escape from linear defect, first emerges near the surface and then propagates within the specimen due to vortex elasticity. THEORY We shall analyze expression for the energy functional of elastic vortex string in a potential well U(s) produced by c-oriented extended linear defect in 3D anisotropic superconductor in the presence of transport Meissner current j(z) = j0exp[z/λ] (z < 0, λ is th
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