Classification of Dirac points with higher-order Fermi arcs

TL;DR

This paper classifies higher order Fermi arcs in Dirac semimetals with rotation symmetry, revealing their dependence on Dirac point linearity and symmetry group, and predicts their presence in Na$_3$Bi.

Contribution

It provides a systematic classification of higher order Fermi arcs in Dirac semimetals protected by rotation and combined symmetries, including models and predictions.

Findings

Linear Dirac points exhibit higher order Fermi arcs

Quadratic Dirac points lack higher order Fermi arcs

Higher order Fermi arcs follow $$ or $$ group structures

Abstract

Dirac semimetals lack a simple bulk-boundary correspondence. Recently, Dirac materials with four-fold rotation symmetry have been shown to exhibit a higher order bulk-hinge correspondence: they display "higher order Fermi arcs," which are localized on hinges where two surfaces meet and connect the projections of the bulk Dirac points. In this paper, we classify higher order Fermi arcs for Dirac semimetals protected by a rotation symmetry and the product of time-reversal and inversion. Such Dirac points can be either linear in all directions or linear along the rotation axis and quadratic in other directions. By computing the filling anomaly for momentum-space planes on either side of the Dirac point, we find that all linear Dirac points exhibit higher order Fermi arcs terminating at the projection of the Dirac point, while the Dirac points that are quadratic in two directions lack such higher order Fermi arcs. When higher order Fermi arcs do exist, they obey either a $\mathbb{Z}_2$ (four-fold rotation axis) or $\mathbb{Z}_3$ (three- or six-fold rotation axis) group structure. Finally, we build two models with six-fold symmetry to illustrate the cases with and without higher order Fermi arcs. We predict higher order Fermi arcs in Na$_3$Bi.