Topological gimbal phonons in T-carbon

TL;DR

This paper reports the discovery of topological nodal gimbal phonons, including Weyl phonons, in T-carbon, revealing complex topological phonon states and surface phenomena in a simple carbon allotrope.

Contribution

First demonstration of topological nodal gimbal and Weyl phonons in T-carbon, expanding the understanding of topological phonons in real materials.

Findings

Presence of three intersecting nodal gimbal phonons around Γ point.

Existence of type-I Weyl phonons near X points.

Existence of type-II Weyl phonons around L points.

Abstract

The topological metal states in electronic systems have been extensively studied, but topological phonons were explored only in few examples so far. Here, we expose for the first time that the topological nodal gimbal phonons, type-I and type-II Weyl phonons are simultaneously present in T-carbon, a recently realized new allotrope of carbon. At about 15.2 THz, we find that there exist three mutually intersecting nodal loops (named as nodal gimbal phonons) around {\Gamma} point, and two pairs of type-I Weyl phonons on the boundary of Brillouin zone around each X point. In addition, there exist three pairs of type-II Weyl phonons at about 14.5 THz around each L point. It is shown that these exotic topological phonons are protected by corresponding symmetries, and lead to topologically nontrivial surface states. Our findings not only afford plenty of intriguing topological phonon states in a simple material like T-carbon but also provide a new platform to study novel properties of topological phonons, which would facilitate further both experimental and theoretical works in future.