Vortex Structure and Anisotropic Superconducting Gaps in Ba[Fe(Ni)]$_2$As$_2$

TL;DR

This study investigates the vortex structure and anisotropic superconducting gaps in Ni-doped BaFe$_{2}$As$_2$, revealing two distinct gaps with moderate anisotropy and evidence of strong coupling in the larger gap, using magnetization and spectroscopy techniques.

Contribution

It provides direct measurements of two superconducting gaps and their anisotropy in Ni-doped BaFe$_2$As$_2$, advancing understanding of its superconducting properties.

Findings

Identification of two distinct superconducting gaps with moderate anisotropy.

Evidence of strong coupling in the larger superconducting gap.

Determination of critical current density and vortex pinning characteristics.

Abstract

We studied nearly optimally Ni-substituted BaFe$_{2-x}$Ni$_x$As$_2$ (BFNA) single crystals with $T_C \approx 18.5$\,K. In irreversible magnetization measurements, we determined the field dependence of the critical-current density and discuss the nature of observed strong bulk pinning. Using intrinsic multiple Andreev reflections effect (IMARE) spectroscopy, we directly determine two distinct superconducting gaps and resolve their moderate anisotropy in the momentum space. The BCS-ratio for the large gap $2\Delta_L/k_BT_C > 4.1$ evidences for a strong coupling in the $\Delta_L$-bands.