Multifractal scaling of flux penetration in the Iron-based Superconductor Ba(Fe$_{0.93}$Co$_{0.07}$)$_{2}$As$_2$

TL;DR

This study investigates the complex, multi-fractal scaling behavior of magnetic flux penetration in an iron-based superconductor, revealing anomalous roughening properties and proposing a vortex penetration model based on percolation theory.

Contribution

It uncovers multi-fractal scaling and non-Gaussian correlations in flux front roughening, advancing understanding of vortex dynamics in disordered superconductors.

Findings

Multi-fractal behavior in flux front roughening

Independence of exponents from temperature

Distinct scaling from avalanche-mediated flux penetration

Abstract

The penetration of magnetic flux fronts in the optimally-doped iron-based superconductor Ba(Fe$_{1-x}$Co$_{x}$)$_{2}$As$_2$ ($x = 0.07 \pm 0.005$) is studied by means of magneto-optical imaging and Bitter decoration. The higher-order analysis of roughening and growth of the magnetic flux front reveals anomalous scaling properties, indicative of non-Gaussian correlations of the disorder potential. While higher-order spatial correlation functions reveal multi-fractal behavior for the roughening, the usual Kardar-Parisi-Zhang growth exponent is found. Both exponents are found to be independent of temperature. The scaling behavior is manifestly different from that found for other modes of flux penetration, such as that mediated by avalanches, suggesting that multi-scaling is a powerful tool for the characterization of roughened interfaces. We propose a scenario for vortex penetration based on two-dimensional percolation and cluster aggregation for an inhomogeneously disordered superconductor.