Two-gap superconductivity with line nodes in CsCa2Fe4As4F2

Journal article

We report the results of a muon-spin rotation ($\mu$SR) experiment to determine the superconducting ground state of the iron-based superconductor $CsCa_2Fe_4As_4F_2$ with $T_{\rm c} \approx 28.3\,K$. This compound is related to the fully-gapped superconductor $CaCsFe_4As_4$, but here the Ca-containing spacer layer is replaced with one containing $Ca_2F_2$. 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 $\lambda_{ab}(T=0)=423(5)\,nm$.

Authors: Kirschner, F; Adroja, D; Wang, Z; Lang, F; Smidman, M

• Publication status: Published
• Peer review status: Peer reviewed
• Publisher: American Physical Society
• Journal: Physical Review B
• Volume: 97
• Issue: 6
• Article number: 060506(R)
• Publication date: 2018-02-20
• Acceptance date: 2018-02-08
• DOI: 10.1103/PhysRevB.97.060506
• ISSN: 2469-9950
• Keywords: Rapid Communication