Interplay between p- and d- orbitals yields multiple Dirac states in one- and two-dimensional CrB4

TL;DR

This study predicts multiple Dirac states in monolayered CrB4 due to p- and d-orbital interactions, revealing its semimetallic nature and Dirac fermions in nanoribbons through ab initio calculations.

Contribution

It provides the first theoretical evidence of multiple Dirac cones in CrB4, highlighting the orbital interplay and their manifestation in one- and two-dimensional geometries.

Findings

Six inequivalent Dirac cones identified in monolayer CrB4

CrB4 is a semimetal with electron-hole pockets

Dirac points persist in nanoribbons, indicating massless fermions

Abstract

Theoretical evidence of the existence of six inequivalent and six threefold degenerate pairs of Dirac cones in the low-spectrum diagram of monolayered hexagonal CrB4 is provided. The four d-electrons of the Cr atom are yielded to the B sublattices creating an isoelectronic structure to graphene where the interplay between p- and d- orbitals leads to the appearance of additional Dirac states on both one- and two-dimensional geometries. Ab initio calculations show that, although spin-orbit interaction splits the cone-shaped valence and conduction bands, CrB4 is a semimetal with compensated electron-hole pockets. As the two-dimensional layer is shaped into finite-width ribbons, one actual and one symmetry-frustrated Dirac point are observed at the Fermi level, yielding massless fermions in a one-dimensional nano-structure with no topological insulating features. A rational explanation in terms of periodic boundary conditions across the ribbon axis is given to unveil the origin of the Dirac point.