Direct Visualization of the Nematic Superconductivity in CuxBi2Se3

Ran Tao,Xi Liu,Ya-Jun Yan,Dong-Lai Feng,Qiang-Hua Wang,Yoichi Ando,Tong Zhang,Zhi-Wei Wang

doi:10.1103/physrevx.8.041024

Abstract

Cu$_x$Bi$_2$Se$_3$ hosts both topological surface states and bulk superconductivity. It has been identified recently as a topological superconductor (TSC) with an extraordinary nematic, i. e. C2-symmetric, superconducting state and odd-parity pairing. Here, using scanning tunneling microscopy (STM), we directly examine the response of the superconductivity of CuxBi2Se3 to magnetic field. Under out-of-plane fields, we discover elongated magnetic vortices hosting zero-bias conductance peaks consistent with the Majorana bound states expected in a TSC. Under in-plane fields, the average superconducting gap exhibits two-fold symmetry with field orientation; the long C2 symmetry axes are pinned to the dihedral mirror planes under B//=0.5 T but rotate slightly under B//=1.0 T. Moreover, a nodeless {\Delta}4x gap structure is semi-quantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in CuxBi2Se3 and pose strong constraints on theory.

Highlights

Topological superconductors, as host of Majorana fermions and Majorana zero modes (MZMs) [1], may facilitate topological quantum computing
Under out-of-plane fields (B⊥), we discover elongated magnetic vortices hosting zero-bias conductance peaks consistent with the Majorana bound states expected in a topological superconductor (TSC)
Unlike the theoretical triumph in predicting topological insulators [1,3], metals, and semimetals, theory and experiment diverge when it comes to TSCs

Summary

Introduction

Topological superconductors, as host of Majorana fermions and Majorana zero modes (MZMs) [1], may facilitate topological quantum computing. In practice, topological superconductors (TSCs) are rare. Among the various recipes for making a TSC [1,2], bulk superconductors that host topological surface states are the most natural candidates. Unlike the theoretical triumph in predicting topological insulators [1,3], metals, and semimetals, theory and experiment diverge when it comes to TSCs. there is a large gap in our understanding of TSCs, and in particular, details of the microscopic behavior of TSCs are in urgent demand for improving theory

Methods

Results

Conclusion