Three-dimensional honeycomb carbon: Junction line distortion and novel emergent fermions

TL;DR

This paper introduces a new three-dimensional carbon allotrope, hC28, which exhibits exceptional stability and hosts multiple types of unconventional emergent fermions, opening new avenues for fundamental research and applications.

Contribution

The study proposes a novel 3D carbon allotrope, hC28, with unique electronic properties including multiple emergent fermions, supported by first-principles calculations.

Findings

hC28 is more stable than many other carbon allotropes.

It hosts multiple unconventional emergent fermions.

The material is thermally stable at high temperatures.

Abstract

Carbon enjoys a vast number of allotropic forms, each possessing unique properties determined by the lattice structures and bonding characters. Here, based on first-principles calculations, we propose a new three-dimensional carbon allotrope--hC28. We show that hC28 possesses exceptional energetic, dynamical, thermal, and mechanical stability. It is energetically more stable than most other synthesized or proposed carbon allotropes. The material has a relatively small bulk modulus, but is thermally stable at temperatures as high as 2000 K. The structural, mechanical, x-ray diffraction, and electronic properties are systematically investigated. Particularly, we show that its low-energy band structure hosts multiple unconventional emergent fermions, including the quadratic-contact-point fermions, the birefringent Dirac fermions, and the triple-point fermions. We construct effective models to characterize each kind of fermions. Our work not only discovers a new carbon allotropic form, it also reveals remarkable mechanical and electronic properties for this new material, which may pave the way towards both fundamental studies as well as practical applications.