Surface morphology and electronic structure in stoichiometric superconductor CaKFe_(4)As_(4) robed by scanning tunneling microscopy/spectroscopy

作     者：Xiaodong Yu Zhongxu Wei Zhanyi Zhao Tao Xie Chang Liu Ge He Qihong Chen Lei Shan Huiqian Luo Qing Huan Jie Yuan Kui Jin Xiaodong Yu;Zhongxu wei;Zhanyi Zhao;Tao Xie;Chang Liu;Ge He;Qihong Chen;Lei Shan;Huiqian Luo;Qing Huan;Jie Yuan;Kui Jin

作者机构：Beijing National Laboratory for Condensed Matter PhysicsInstitute of PhysicsChinese Academy of SciencesBeijing 100190China School of Physical SciencesUniversity of Chinese Academy of SciencesBeijing 100049China Walther Meissner InstituteBayerische Akademie der WissenschaftenGarching 85748Germany Key Laboratory of Structure and Functional Regulation of Hybrid Materials of Ministry of EducationInstitutes of Physical Science and Information TechnologyAnhui UniversityHefei 230601China Songshan Lake Materials LaboratoryDongguan 523808China 

出 版 物：《Science China(Physics,Mechanics & Astronomy)》 (中国科学：物理学、力学、天文学（英文版）)

年 卷 期：2021年第64卷第12期

页      面：144-150页

核心收录：

学科分类：07[理学] 070205[理学-凝聚态物理] 0702[理学-物理学] 

基　　金：supported by the National Key Basic Research Program of China(Grant Nos.2017YFA0302902,2016YFA0300301,2017YFA0303003,and 2018YFB0704102) the National Natural Science Foundation of China(Grant Nos.11927808,11834016,118115301,119611410,11961141008,11822411,and 11961160699) the Key Research Program of Frontier Sciences,Chinese Academy of Sciences(Grant Nos.QYZDBSSW-SLH008,and QYZDY-SSW-SLH001) the Strategic Priority Research Program(B)of Chinese Academy of Sciences(Grant Nos.XDB25000000,and XDB33000000) the Beijing Natural Science Foundation(Grant Nos.Z190008,and JQ19002) the Key-Area Research and Development Program of Guangdong Province(Grant No.2020B0101340002) the CAS Interdisciplinary Innovation Team support from the Youth Innovation Promotion Association of CAS(Grant No.Y202001)。 

主　　题：CaKFe_(4)As_(4) scanning tunneling microscopy surface reconstructions superconductivity 

摘      要：CaKFe_(4)As_(4) is a new-type superconductor with a relatively high transition temperature of 35 K among stoichiometric iron-based superconductors. Based on scanning tunneling microscopy/spectroscopy, the surface morphology and electronic structure of CaKFe_(4)As_(4) single crystal were systematically investigated. The cleaved CaKFe_(4)As_(4) showed various morphologies, such as atomically resolved 1×1, 1×2, and √2×√2 lattices. By analyzing the geometrical correlations of these morphologies, the 1×1 and 1×2 lattices were identified as the original and reconstructed As layers, respectively, whereas the √2×√2 lattice was distinguished as the reconstructed alkaline-earth-metal or alkali-metal layer. The superconducting energy gap of 7.3 me V and bosonic mode of 12.7 me V were resolved in the scanning tunneling spectra. In addition, the superconducting energy gaps measured on different terminations were identical and consistent with the values obtained by bulk-sensitive techniques, indicating that the electronic structures of CaKFe_(4)As_(4) were insensitive to the surface reconstructions. Our study clarifies the relationships between complex surface reconstructions and surface terminations and preliminarily presents that there is no obvious effect of surface reconstructions on electronic states.