摘要
As a new type of iron-based superconductor, CaKFe_(4)As_(4) has recently been demonstrated to be a promising platform for observing Majorana zero modes (MZMs). The surface of CaKFe_(4)As_(4) plays an important role in realizing the MZM since it hosts superconducting topological surface states. However, due to the complicated crystal structure, the terminal surface of CaKFe_(4)As_(4) has not been determined yet. Here, by using scanning tunneling microscopy/spectroscopy (STM/S), we find that there are two types of surface structure in CaKFe_(4)As_(4). Bias-dependent atomic resolution images show an evolvement from 2–√×2–√ superstructure with respect to the As lattice into 1 × 1 when the tip is brought close to the surface, revealing the sublattice of missing As atoms. Together with the first-principles calculations, we show that the surface As layer has a buckled structure. Our findings provide insight to future surface study of CaKFe_(4)As_(4) as well as other iron-pnictide superconductors.
基金
We thank Min Ouyang and Wu Zhou for helpful discussion. This work is supported by the National Key Research and Development Program of China (Nos. 2019YFA0308500 and 2018YFA0305800)
the National Natural Science Foundation of China (Nos. 51922011, 51991340, and 61888102)
the Strategic Priority Research Program of Chinese Academy of Sciences (No. XDB28000000)
A portion of the research was performed in CAS Key Laboratory of Vacuum Physics. G. H. C. is supported by Funds for the Central Universities and the National Key Research and Development Program of China (Nos. 2019FZA3004, 2017YFA0303002, and 2016YFA0300202).
