Three-dimensional Dirac Phonons with Inversion Symmetry

TL;DR

This paper systematically investigates the existence and symmetry protection of three-dimensional Dirac phonons in crystalline solids with inversion symmetry, revealing two categories based on their origin and symmetry mechanisms.

Contribution

It provides the first comprehensive analysis of 3D Dirac phonons, classifying them into two categories and highlighting the roles of non-symmorphic and inversion symmetries.

Findings

Two categories of 3D Dirac phonons identified

Dirac points protected by high symmetry points and lines

Non-symmorphic and inversion-time reversal symmetries are crucial

Abstract

Dirac semimetals associated with bulk Dirac fermions are well-known in topological electronic systems. In sharp contrast, three-dimensional (3D) Dirac phonons in crystalline solids are still unavailable. Here we perform symmetry arguments and first-principles calculations to systematically investigate 3D Dirac phonons in all space groups with inversion symmetry. The results show that there are two categories of 3D Dirac phonons depending on their protection mechanisms and positions in momentum space. The first category originates from the four-dimensional irreducible representations at the high symmetry points. The second category arises from the phonon branch inversion, and the symmetry guarantees Dirac points to be located along the high symmetry lines. Furthermore, we reveal that non-symmorphic symmetries and the combination of inversion and time-reversal symmetries play essential roles in the emergence of 3D Dirac phonons. Our work not only offers a comprehensive understanding of 3D Dirac phonons but also provides significant guidance for exploring Dirac bosons in both phononic and photonic systems.