1Beijing National Laboratory for Condensed Matter Physics, Institute of Physics, Chinese Academy of Sciences, Beijing 100190 2School of Physical Sciences, University of Chinese Academy of Sciences, Beijing 100190 3Songshan Lake Materials Laboratory, Dongguan 523808
Abstract：We report a $^{19}\!$F nuclear magnetic resonance (NMR) study on single-crystal KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$ ($T_{\rm c} \sim 33.3$ K). The $^{19}$F NMR spectral shape of KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$ is weakly dependent on temperature and the Knight shift is small, which implies weak coupling between the CaF layer and the FeAs layer. The temperature dependence of 1/$^{19}\!T_{1}$ shows a hump below $T_{\rm c}$, however the 1/$^{75}\!T_{1}$ decreases just below $T_{\rm c}$, which implies that there are strong in-plane magnetic fluctuations in the CaF layers than in the FeAs layers. This may be caused by the motion of vortices. The absence of the coherence peak suggests unconventional superconductivity in KCa$_{2}$Fe$_{4}$As$_{4}$F$_{2}$.
Liu Y, Liu Y B , Tang Z T , Jiang H, Wang Z C , Ablimit A, Jiao W H , Tao Q, Feng C M , Xu Z A and Cao G H 2016 Phys. Rev. B93 214503
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Kaluarachchi U S, Taufour V, Sapkota A, Borisov V, Kong T, Meier W R, Kothapalli K, Uel, B G, Kreyssig A, Valentí R, McQueeney R J, Goldman A I, Bud'ko S L and Canfield P C 2017 Phys. Rev. B96 140501
2019, Vol. 36 
