Material realization of spinless, covalent-type Dirac semimetals in three dimensions

Graphene, known as a two-dimensional Dirac semimetal, has attracted great attention in condensed matter physics both for its fundamental and applied significance, owing to its exceptionally clean electronic band structure and topological phenomena such as the quantum Hall effect. Three-dimensional (3D) Dirac semimetals have been regarded as 3D analogues of graphene; however, in conventional 3D Dirac semimetals, where the Dirac state originates from spin–orbit coupling, the linear energy dispersion is asymmetric, unlike in graphene.

In this study, we realized a true three-dimensional analogue of graphene by employing a newly proposed 3D Dirac semimetal, R₈CoX₃, reported in 2024. In R₈CoX₃, the Dirac semimetal state emerges from covalent bonding rather than spin–orbit coupling, leading to an electron–hole symmetric linear energy dispersion similar to that of graphene. Moreover, the compound allows chemical substitution, and its combination with a symmetric dispersion structure offers the potential for various quantum phenomena. In this talk, we will demonstrate that substitution at the rare-earth site enables bandwidth control, resulting in enhanced carrier mobility.