Robust and Clean Majorana Zero Mode in the Vortex Core of High-Temperature Superconductor (Li0.84Fe0.16)OHFeSe

Qin Liu,Xiao-Li Dong,Qiang-Hua Wang,Chen-Hao-Ping Wen,Jin-Peng Tian,Tong Zhang,Ya-Jun Yan,Dong-Lai Feng,Zhong-Xian Zhao,Wei-Cheng Bao,Guang-Wei Wang,Rui Peng,Xia Lou,Chen Chen,Zhi-Ping Yin,Yu-Long Huang

doi:10.1103/physrevx.8.041056

Abstract

The Majorana fermion, which is its own anti-particle and obeys non-abelian statistics, plays a critical role in topological quantum computing. It can be realized as a bound state at zero energy, called a Majorana zero mode (MZM), in the vortex core of a topological superconductor, or at the ends of a nanowire when both superconductivity and strong spin orbital coupling are present. A MZM can be detected as a zero-bias conductance peak (ZBCP) in tunneling spectroscopy. However, in practice, clean and robust MZMs have not been realized in the vortices of a superconductor, due to contamination from impurity states or other closely-packed Caroli-de Gennes-Matricon (CdGM) states, which hampers further manipulations of Majorana fermions. Here using scanning tunneling spectroscopy, we show that a ZBCP well separated from the other discrete CdGM states exists ubiquitously in the cores of free vortices in the defect free regions of (Li0.84Fe0.16)OHFeSe, which has a superconducting transition temperature of 42 K. Moreover, a Dirac-cone-type surface state is observed by angle-resolved photoemission spectroscopy, and its topological nature is confirmed by band calculations. The observed ZBCP can be naturally attributed to a MZM arising from this chiral topological surface states of a bulk superconductor. (Li0.84Fe0.16)OHFeSe thus provides an ideal platform for studying MZMs and topological quantum computing.

Highlights

In recent years, many recipes have been proposed for realizing Majorana zero mode (MZM) [1,2,3], as a critical step towards topological quantum computation [4,5]
We conduct density functional theory (DFT) and dynamical mean field theory (DMFT) calculations and ARPES measurements on ðLi0.84Fe0.16ÞOHFeSe, and we find nontrivial band inversion and topological surface states
Without spin-orbital coupling (SOC), the Fe 3dxz and 3dyz bands are degenerate at the Γ point and are in the Γþ5 states, whereas the dispersive Se 4pz band is in the odd Γ−2 state at the Γ point

Summary

INTRODUCTION

Many recipes have been proposed for realizing MZMs [1,2,3], as a critical step towards topological quantum computation [4,5]. Chiral p-wave superconductors are extremely scarce, but Fu and Kane have proposed that proximity effects from an s-wave superconductor on topological surface states would produce a two-dimensional system whose Hamiltonian effectively resembles a spinless p Æ ip superconductor, and it can host Majorana bound states in its vortices [15] (the spinless nature is due to the fact that the topological surface state is spin nondegenerate) Based on this scenario, ZBCPs that may potentially correspond to MZMs have been found in the vortex cores of topological insulator-superconductor heterostructures (e.g., Bi2Te3=NbSe2 and Bi2Te3=FeTexSe1−x) [16,17,18], and topological surface states of bulk superconductors (e.g., CuxBi2Se3 and FeTexSe1−x) [19,20,21,22]. A zero-bias impurity state was observed on interstitial Fe, which is insensitive to the magnetic field [23], but whether this is related to a MZM is yet to be confirmed

A ZBCP can be observed in a fraction of vortices in certain

Electronic structure calculations and ARPES measurements

Core states of impurity-pinned vortices

DISCUSSION AND CONCLUSION