Depinning at the initial stage of the resistive transition in superconductors with a fractal cluster structure

TL;DR

This paper investigates how fractal structures of normal phase clusters in percolative superconductors influence vortex depinning and the onset of resistive behavior, revealing that higher fractal dimensions broaden initial dissipation.

Contribution

It introduces a model linking fractal cluster geometry to vortex depinning and resistive transition characteristics in superconductors.

Findings

Increased fractal dimension broadens the initial dissipation region.

Higher fractal dimension increases free vortex density.

Dependencies of vortex density on fractal boundary dimension are established.

Abstract

Depinning of vortices in percolative superconductor containing fractal clusters of a normal phase is considered. Transition of the superconductor into a resistive state corresponds to the percolation transition from a pinned vortex state to a resistive state when the vortices are free to move. The motion of the magnetic flux transferred by these vortices gives rise to the region of initial dissipation on current-voltage characteristic. The influence of normal phase clusters on distinctive features of current-voltage characteristics of percolative type-II superconductors is considered. It is found that an increase in the fractal dimension of the normal phase clusters causes the initial dissipation region to broaden out. The reason of this effect is an increase in the density of free vortices broken away from the pinning centers by the Lorentz force. Dependencies of the free vortex density on the fractal dimension of the normal phase cluster boundaries are obtained.