Crossover between Anomalous Peak Effects Induced by Splayed and Tilted Columnar Defects in Ba$_{0.6}$K$_{0.4}$Fe$_2$As$_2$

TL;DR

This study explores how different configurations of columnar defects in Ba0.6K0.4Fe2As2 influence the anomalous peak effects in critical current density under magnetic fields, revealing a crossover behavior explained by a proposed model.

Contribution

It introduces and compares the effects of splayed, tilted, and asymmetric columnar defects on the peak behavior of critical current density in a superconductor.

Findings

Non-monotonic Jc dependence on magnetic field observed.

Anomalous peak effect varies with defect configuration.

A model explains the behavior across different defect types.

Abstract

We investigated the magnetic field dependence of the critical current density (Jc) in Ba0.6K0.4Fe2As2 with various configurations of columnar defects (CDs) introduced by 2.6 GeV U or 320 MeV Au irradiations. Splayed CDs are introduced by crossing CDs at a specific angle with respect to the c-axis, while tilted CDs are introduced by irradiating the sample from the direction tilted from the !-axis. We also prepared samples with asymmetric splayed CDs, which bridge the splayed CDs and the tilted CDs, by starting from the tilted CDs and adding CDs along the symmetric direction with respect to the !-axis. In all cases, non-monotonic magnetic field dependence of Jc, which we call anomalous peak effect, is observed at some fraction of the matching field when the magnetic field is applied along the specific direction depending on the configuration of CDs. We propose a model that explains the behavior of the anomalous peak effect in samples with different configuration of CDs.