Observation of a Dirac nodal line in AlB2

TL;DR

This study uses angle-resolved photoemission spectroscopy to reveal a Dirac nodal line in AlB2, providing insights into its topological properties and potential for superconductivity research.

Contribution

First direct observation of a Dirac nodal line in AlB2, linking its electronic structure to topological phenomena and superconductivity potential.

Findings

Identified a Dirac nodal line along the KH line in AlB2

Demonstrated AlB2's band structure as a heavily electron-doped MgB2

Suggested AlB2 as a platform for topological superconductor studies

Abstract

We have performed angle-resolved photoemission spectroscopy of AlB2 which is isostructural to high-temperature superconductor MgB2. Using soft-x-ray photons, we accurately determined the three-dimensional bulk band structure and found a highly anisotropic Dirac-cone band at the K point in the bulk hexagonal Brillouin zone. This band disperses downward on approaching the H point while keeping its degeneracy at the Dirac point, producing a characteristic Dirac nodal line along the KH line. We also found that the band structure of AlB2 is regarded as a heavily electron-doped version of MgB2 and is therefore well suited for fully visualizing the predicted Dirac nodal line. The present results suggest that (Al,Mg)B2 system is a promising platform for studying the interplay among Dirac nodal line, carrier doping, and possible topological superconducting properties.