1 0 O ct 2 01 9 Strong Pauli paramagnetic effect in the upper critical field of KCa 2 Fe 4 As

Teng Wang, 2, 3 Chi Zhang, 2, 4 Liangcai Xu, Jinhua Wang, Shan Jiang, Zengwei Zhu, Zhaosheng Wang, Jianan Chu, 2, 4 Jiaxin Feng, 2, 4 Lingling Wang, Wei Li, Tao Hu, 2 Xiaosong Liu, 2, 3 and Gang Mu 2, ∗ State Key Laboratory of Functional Materials for Informatics, Shanghai Institute of Microsystem and Information Technology, Chinese Academy of Sciences, Shanghai 200050, China CAS Center for Excellence in Superconducting Electronics(CENSE), Shanghai 200050, China School of Physical Science and Technology, ShanghaiTech University, Shanghai 201210, China University of Chinese Academy of Science, Beijing 100049, China Wuhan National High Magnetic Field Center and School of Physics, Huazhong University of Science and Technology, Wuhan 430074, China Anhui Province Key Laboratory of Condensed Matter Physics at Extreme Conditions, High Magnetic Field Laboratory of the Chinese Academy of Sciences, Hefei 230031, China Department of Physics and State Key Laboratory of Surface Physics, Fudan University, Shanghai 200433, China