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arXiv · 1712.04436

Two-gap superconductivity with line nodes in CsCa$_2$Fe$_4$As$_4$F$_2$

Franziska K. K. Kirschner·Devashibhai T. Adroja·Zhi-Cheng Wang·Franz Lang·Michael Smidman·Peter J. Baker·Guang-Han Cao·Stephen J. Blundell
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Abstract

We report the results of a muon-spin rotation ($μ$SR) experiment to determine the superconducting ground state of the iron-based superconductor CsCa$_2$Fe$_4$As$_4$F$_2$ with $T_{\rm c} \approx 28.3\,$K. This compound is related to the fully-gapped superconductor CaCsFe$_4$As$_4$, but here the Ca-containing spacer layer is replaced with one containing Ca$_2$F$_2$. The temperature evolution of the penetration depth strongly suggests the presence of line nodes and is best modelled by a system consisting of both an $s$- and a $d$-wave gap. We also find a potentially magnetic phase which appears below $\approx 10\,$K but does not appear to compete with the superconductivity. This compound contains the largest alkali atom in this family of superconductors and our results yield a value for the in-plane penetration depth of $λ_{ab}(T=0)=423(5)\,$nm.

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Franziska K. K. Kirschner, Devashibhai T. Adroja, Zhi-Cheng Wang, Franz Lang, Michael Smidman, Peter J. Baker, Guang-Han Cao, Stephen J. Blundell. 2018-02-20. Two-gap superconductivity with line nodes in CsCa$_2$Fe$_4$As$_4$F$_2$. https://doi.org/10.1103/physrevb.97.060506

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