Nodal multigap superconductivity in the anisotropic iron-based compound RbCa2Fe4As4F2

TL;DR

This study reveals nodal multigap superconductivity with anisotropic properties in RbCa2Fe4As4F2, a recently discovered iron-based superconductor, using spectroscopic and resonator techniques to analyze its gap structure and anisotropy.

Contribution

It provides the first detailed characterization of the gap structure and anisotropy in RbCa2Fe4As4F2, identifying nodal multigap features and their persistence with Ni doping.

Findings

Identification of two superconducting gaps with d-wave-like nodal structures.

Observation of large London penetration depth anisotropy.

Nodal features remain stable upon Ni doping.

Abstract

The 12442 compounds are a recently discovered family of iron-based superconductors, that share several features with the cuprates due to their strongly anisotropic structure, but are so far poorly understood. Here, we report on the gap structure and anisotropy of RbCa2(Fe1-xNix)4As4F2 single crystals, investigated by a combination of directional point-contact Andreev-reflection spectroscopy and coplanar waveguide resonator measurements. Two gaps were identified, with clear signatures of d-wave-like nodal structures which persist upon Ni doping, well described by a two-band d-d state with symmetry-imposed nodes. A large London penetration depth anisotropy was revealed, weakly dependent on temperature and fully compatible with the d-d model.