Local Measurements of the Superconducting Pairing Symmetry in CuxBi2Se3

TL;DR

This study uses scanning tunneling spectroscopy to investigate the superconducting gap in CuxBi2Se3, revealing a fully gapped s-wave superconductor contrary to prior expectations of topological pairing.

Contribution

It provides direct local measurements showing CuxBi2Se3 behaves as a conventional s-wave superconductor, challenging previous topological superconductor predictions.

Findings

Density of states at Fermi level is fully gapped.

Spectrum fits BCS theory with momentum-independent order parameter.

Contradicts earlier expectations of topological pairing in CuxBi2Se3.

Abstract

Topological superconductors represent a newly predicted phase of matter that is topologically distinct from conventional superconducting condensates of Cooper pairs. As a manifestation of their topological character, topological superconductors support solid-state realizations of Majorana fermions at their boundaries. The recently discovered superconductor CuxBi2Se3 has been theoretically proposed as an odd-parity superconductor in the time-reversal-invariant topological superconductor class and point-contact spectroscopy measurements have reported the observation of zero-bias conductance peaks corresponding to Majorana states in this material. Here we report scanning tunneling spectroscopy (STS) measurements of the superconducting energy gap in CuxBi2Se3 as a function of spatial position and applied magnetic field. The tunneling spectrum shows that the density of states at the Fermi level is fully gapped without any in-gap states. The spectrum is well described by the Bardeen-Cooper-Schrieffer (BCS) theory with a momentum independent order parameter, which suggests that Cu0.2Bi2Se3 is a classical s-wave superconductor contrary to previous expectations and measurements.