Gap Structure of 12442-Type KCa$_2$(Fe$_{1-x}$Co$_{x}$)$_4$As$_{4}$F$_2$ ($x$ = 0, 0.1) Revealed by Temperature Dependence of Lower Critical Field
Jianan Chu1,2,3, Teng Wang1,2,4, Han Zhang1,2,3, Yixin Liu1,2,3, Jiaxin Feng1,2,3, Zhuojun Li1,2, Da Jiang1,2,3, Gang Mu1,2,3*, Zengfeng Di1,3, and Xiaoming Xie1,2,3
1State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China 2CAS Center for Excellence in Superconducting Electronics (CENSE), Shanghai 200050, China 3University of Chinese Academy of Sciences, Beijing 100049, China 4School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China
Abstract：We report an in-depth investigation on the out-of-plane lower critical field $H_{\rm c1}$ of the KCa$_2$(Fe$_{1-x}$Co$_{x}$)$_4$As$_{4}$F$_2$ (12442-type, $x$ = 0, 0.1). The multi-gap feature is revealed by the kink in the temperature-dependent $H_{\rm c1}(T)$ curve for the two samples with different doping levels. Based on a simplified two-gap model, the magnitudes of the two gaps are determined to be $\varDelta_1$ = 1.2 meV and $\varDelta_2$ = 5.0 meV for the sample with $x$ = 0, $\varDelta_1$ = 0.86 meV and $\varDelta_2$ = 2.8 meV for that with $x$ = 0.1. With the cobalt doping, the ratio of energy gap to critical transition temperature ($\varDelta/k_{\rm B}T_{\rm c}$) remains almost unchanged for the smaller gap and is suppressed by 20% for the larger gap. For the undoped KCa$_2$Fe$_4$As$_{4}$F$_2$, the obtained gap sizes are generally consistent with the results of angle-resolved photoemission spectroscopy experiments.
(Mixed states, critical fields, and surface sheaths)
引用本文:
. [J]. 中国物理快报, 2020, 37(12): 127401-.
Jianan Chu, Teng Wang, Han Zhang, Yixin Liu, Jiaxin Feng, Zhuojun Li, Da Jiang, Gang Mu, Zengfeng Di, and Xiaoming Xie. Gap Structure of 12442-Type KCa$_2$(Fe$_{1-x}$Co$_{x}$)$_4$As$_{4}$F$_2$ ($x$ = 0, 0.1) Revealed by Temperature Dependence of Lower Critical Field. Chin. Phys. Lett., 2020, 37(12): 127401-.
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