Material laws and related uncommon phenomena in the electromagnetic response of type-II superconductors in longitudinal geometry

TL;DR

This paper presents a theoretical analysis of the electromagnetic response of type-II superconductors in longitudinal geometry, revealing phenomena like negative current patterns and internal anisotropy effects under various magnetic field conditions.

Contribution

It introduces a comprehensive theoretical framework for understanding flux cutting, depinning, and anisotropic effects in superconductors under longitudinal magnetic fields, including novel predictions of current patterns.

Findings

Negative current patterns observed

Transport current enhancement at sample center

Correlation between current evolution and paramagnetic peaks

Abstract

Relying on our theoretical approach for the superconducting critical state problem in 3D magnetic field configurations, we present an exhaustive analysis of the electrodynamic response for the so-called longitudinal transport problem in the slab geometry. A wide set of experimental conditions have been considered, including modulation of the applied magnetic field either perpendicular or parallel (longitudinal) to the transport current density. The main objective of our work was to characterize the role of the macroscopic material law that should properly account for the underlying mechanisms of flux cutting and depinning. The intriguing occurrence of negative current patterns and the enhancement of the transport current flow along the center of the superconducting sample are reproduced as a straightforward consequence of the magnetically induced internal anisotropy. Moreover, we show that related to a maximal projection of the current density vector onto the local magnetic field, a maximal transport current density occurs somewhere within the sample. The elusive measurement of the flux cutting threshold (critical value of such parallel component $J_{c ||}$) is suggested on the basis of local measurements of the transport current density. Finally, we show that a high correlation exists between the evolution of the transport current density and the appearance of paramagnetic peak structures in terms of the applied longitudinal magnetic field.