Topological superconducting phase in high-Tc superconductor MgB2 with Dirac-nodal-line fermions

TL;DR

This paper reports the discovery of a topological Dirac-nodal-line state in high-temperature superconductor MgB2, which can host Majorana fermions at relatively high temperatures, opening new avenues for experimental studies.

Contribution

The study reveals a topological Dirac-nodal-line state in MgB2 and demonstrates the potential for high-temperature topological superconductivity with Majorana fermions.

Findings

Identification of a Dirac-nodal-line in MgB2

Topological edge states with chiral modes observed

Potential for high-temperature Majorana fermion experiments

Abstract

Topological superconductors are an intriguing and elusive quantum phase, characterized by topologically protected gapless surface/edge states residing in a bulk superconducting gap, which hosts Majorana fermions. Unfortunately, all currently known topological superconductors have a very low transition temperature, limiting experimental measurements of Majorana fermions. Here we discover the existence of a topological Dirac-nodal-line state in a well-known conventional high-temperature superconductor, MgB2. First-principles calculations show that the Dirac-nodal-line structure exhibits a unique one-dimensional dispersive Dirac-nodal line, protected by both spatial-inversion and time-reversal symmetry, which connects the electron and hole Dirac states. Most importantly, we show that the topological superconducting phase can be realized with a conventional s-wave superconducting gap, evidenced by the topological edge mode of the MgB2 thin films showing chiral edge states. Our discovery may enable the experimental measurement of Majorana fermions at high temperature.