Self-induced Magnetic Flux Structure in the Magnetic Superconductor RbEuFe$_4$As$_4$

TL;DR

This paper investigates the unusual enhancement of magnetic flux in RbEuFe$_4$As$_4$, revealing how magnetic and superconducting interactions create a self-organized flux structure that defies typical behavior.

Contribution

It uncovers a novel flux boosting mechanism driven by magnetic-superconducting interplay, with direct imaging evidence of flux dynamics in this material.

Findings

Magnetic flux density increases near the magnetic transition temperature.

Magnetic subsystem acts as an internal flux pump.

Superconducting subsystem controls vortex conveyance via a critical state.

Abstract

We report an unusual enhancement of the magnetic induction in single crystals of the magnetic superconductor RbEuFe$_4$As$_4$ , highlighting the interplay between superconducting and magnetic subsystems in this material. Contrary to the conventional Meissner expulsion of magnetic flux below the superconducting transition temperature, we observe a substantial boost of the magnetic flux density upon approaching the magnetic transition temperature, Tm. Direct imaging of the flux evolution with a magneto-optical technique, shows that the magnetic subsystem serves as an internal magnetic flux pump, drawing Abrikosov vortices from the surface, while the superconducting subsystem controls their conveyance into the bulk of the magnetic superconductor via a peculiar self-organized critical state.