Through 2.6 GeV U irradiations, we have induced bimodal splayed columnar defects in Ba1−xKxFe2As2 single crystals with splay angles, ±5∘, ±10∘, ±15∘, and ±20∘. Critical current densities through magnetization measurements were carefully evaluated, where a splay angle of ±5∘ brought about the highest Jc. Mageto-optical images close to Tc indicates highly anisotropic discontinuity lines in the remnant state, and with anisotropy increasing with greater splay angles. Moreover, amongst those with splayed columnar defects, anomalous non-monotonic field dependences of Jc and S with an extrema at some fraction of the matching field are observed. We discuss that such Jc enhancement arises from a field-driven coupling transition in which intervortex interactions reorganize the vortex structure to be accommodated into columnar defects, thereby increasing pinning at higher fields.
@article{arxiv.1802.09868,
title = {Field-driven transition in the Ba$_{1-x}$K$_x$Fe$_2$As$_2$ superconductor with splayed columnar defects},
author = {Akiyoshi Park and Sunseng Pyon and Kengo Ohara and Nozomu Ito and Tsuyoshi Tamegai and Tadashi Kambara and Atsushi Yoshida and Ataru Ichinose},
journal= {arXiv preprint arXiv:1802.09868},
year = {2018}
}