A new Majorana platform in an Fe-As bilayer superconductor

Wenyao Liu,Hong-Jun Gao,Shixuan Du,Ya-Bin Liu,Lingyuan Kong,Hong Ding,Takeshi Kondo,Fazhi Yang,Zhiping Yin,Michał Papaj,Guang-Han Cao,Liang Fu,Peng Zhang,Geng Li,Shiyu Zhu,Guangwei Wang,Shik Shin,Hui Chen,Lu Cao

doi:10.1038/s41467-020-19487-1

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

Introduction

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.

Results

Conclusion