A new Majorana platform in an Fe-As bilayer superconductor.

Liu, Wenyao; Cao, Lu; Zhu, Shiyu; Kong, Lingyuan; Wang, Guangwei; Papaj, Michał; Zhang, Peng; Liu, Ya-Bin et al. · Nat Commun · 2020

basic_science · Level V

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Abstract

Iron-chalcogenide superconductors have emerged as a promising Majorana platform for topological quantum computation. By combining topological band and superconductivity in a single material, they provide significant advantage to realize isolated Majorana zero modes. However, iron-chalcogenide superconductors, especially Fe(Te,Se), suffer from strong inhomogeneity which may hamper their practical application. In addition, some iron-pnictide superconductors have been demonstrated to have topological surface states, yet no Majorana zero mode has been observed inside their vortices, raising a question of universality about this new Majorana platform. In this work, through angle-resolved photoemission spectroscopy and scanning tunneling microscopy/spectroscopy measurement, we identify Dirac surface states and Majorana zero modes, respectively, for the first time in an iron-pnictide superconductor, CaKFe<sub>4</sub>As<sub>4</sub>. More strikingly, the multiple vortex bound states with integer-quantization sequences can be accurately reproduced by our model calculation, firmly establishing Majorana nature of the zero mode.