Observation of Topological Surface State in High Temperature Superconductor MgB2

TL;DR

This paper reports the discovery of topological surface states in MgB2, a high-temperature superconductor with Tc=39K, using ARPES, suggesting MgB2 as a promising platform for topological superconductivity research.

Contribution

The study provides the first evidence of Dirac Nodal Lines and topological surface states in MgB2, a superconductor with a record high Tc among candidates.

Findings

Presence of Dirac Nodal Lines and topological surface states in MgB2

MgB2's high Tc of 39K surpasses previous topological superconductor candidates

Topological states in MgB2 are highly tolerant to disorder and doping variations

Abstract

The hunt for the benchmark topological superconductor (TSc) has been an extremely active research subject in condensed matter research, with quite a few candidates identified or proposed. However, low transition temperatures (Tc) and/or strong sensitivity to disorder and dopant levels in known TSc candidates have greatly hampered progress in this field. Here, we use Angle-resolved Photoemission Spectroscopy (ARPES) to show the presence of Dirac Nodal Lines (DNLs) and the corresponding topological surface states (TSS's) on the [010] faces of the Tc=39K s-wave BCS superconductor MgB2. Not only is this nearly triple the current record of superconducting Tc among all candidate TSc's, but the nature of these DNL states should make them highly tolerant against disorder and inadvertent doping variations. This makes MgB2 a promising high temperature platform for the study of topological superconductivity.