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.
@article{arxiv.1807.01426,
title = {Observation of a Dirac nodal line in AlB2},
author = {Daichi Takane and Seigo Souma and Kosuke Nakayama and Takechika Nakamura and Hikaru Oinuma and Kentaro Hori and Kouji Horiba and Hiroshi Kumigashira and Noriaki Kimura and Takashi Takahashi and Takafumi Sato},
journal= {arXiv preprint arXiv:1807.01426},
year = {2018}
}