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, CaKFe4As4. 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.
Highlights
Iron-chalcogenide superconductors have emerged as a promising Majorana platform for topological quantum computation
Applying angle-resolved photoemission spectroscopy (ARPES) and the density functional theory (DFT) plus dynamical mean field theory (DMFT) calculation, our investigation indicates that the glide-mirror symmetry breaking together with electron correlations create a topological band inversion in CaKFe4As4
By using scanning tunneling microscopy/spectroscopy (STM/S), we observe Majorana zero modes (MZMs) within integer-quantization sequence of Caroli–de Gennes–Matricon bound states (CBSs) inside a SC vortex core, which is identified as a topological hallmark of MZMs in the previous studies on Fe(Te,Se)[2,9]
Summary
Iron-chalcogenide superconductors have emerged as a promising Majorana platform for topological quantum computation. The calculation of the surface state in CaKFe4As4 (Fig. 2a) shows that the Dirac-cone-type band structure exists inside the SOC gap with its Dirac point above EF, which may obstruct the ARPES technique in observing the Dirac-cone-like feature of the surface state.
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