Direct Visualization of the Nematic Superconductivity in Cu_{x}Bi_{2}Se_{3}

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., C_{2}-symmetric superconducting state and odd-parity pairing. Here, using scanning tunneling microscopy, we directly examine the response of the superconductivity of Cu_{x}Bi_{2}Se_{3} 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 C_{2} 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 Δ_{4x} gap structure is semiquantitatively determined for the first time. Our data paint a microscopic picture of the nematic superconductivity in Cu_{x}Bi_{2}Se_{3} and pose strong constraints on theory.