New Nanoporous Graphyne Monolayer as Nodal Line Semimetal: Double Dirac Points with an Ultrahigh Fermi Velocity

TL;DR

This paper introduces a new stable 2D carbon monolayer called H4,4,4-graphyne with double Dirac points and ultrahigh Fermi velocities, promising for high-speed electronics.

Contribution

The study proposes a novel nanoporous carbon monolayer with unique electronic properties, including double Dirac points and high Fermi velocities, expanding the family of 2D carbon materials.

Findings

H4,4,4-graphyne is thermally stable up to 1500 K.

It exhibits double Dirac points with high Fermi velocities (1.04–1.27×10^6 m/s).

The double Dirac points originate from nodal line states explained by a tight-binding model.

Abstract

Two-dimensional (2D) carbon materials play an important role in nanomaterials. We propose a new carbon monolayer, named hexagonal-4,4,4-graphyne (H4,4,4-graphyne), which is a nanoporous structure composed of rectangular carbon rings and triple bonds of carbon. Using first-principles calculations, we systematically studied the structure, stability, and band structure of this new material. We found that its energy is much lower than that of some experimental carbon materials and it is stable at least up to 1500 K. In contrast to the single Dirac point band structure of other 2D carbon monolayers, the band structure of H4,4,4-graphyne exhibits double Dirac points along the high symmetry points and the corresponding Fermi velocities (1.04~1.27 * 106 m/s) are asymmetric and higher than that of graphene. The origin of these double Dirac points is traced back to the nodal line states, which can be well explained by a tight-binding model. The H4,4,4-graphyne forms a moir\'e superstructure when placed on top of a BN substrate, while keeping the double Dirac points. These properties make H4,4,4-graphyne a promising semimetal material for applications in high-speed electronic devices.