Direct Visualization of the Nematic Superconductivity in CuxBi2Se3

Abstract

CuxBi2Se3 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, we directly examine the response of the superconductivity of CuxBi2Se3 to magnetic field. 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 TSC. Under in-plane fields (B//), the average superconducting gap exhibits twofold 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 Δ4x gap structure is semiquantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in CuxBi2Se3 and pose strong constraints on theory.