Towards Three-Dimensional Weyl-SurfaceSemimetals in Graphene Networks

TL;DR

This paper predicts three-dimensional graphene network structures that host flat Weyl surfaces, demonstrating their topological stability and potential for applications in electronics, energy storage, and catalysis.

Contribution

It introduces novel 3D graphene network structures with Weyl surfaces, supported by first-principles calculations and tight-binding models, expanding the class of topological carbon materials.

Findings

Two flat Weyl surfaces appear in the Brillouin zone of these networks.

The structures are robust against external strain.

Surface passivation induces strong magnetism on the flat bands.

Abstract

Graphene as a two-dimensional (2D) topological Dirac semimetal has attracted much attention for its outstanding properties and potential applications. However, three-dimensional (3D) topological semimetals for carbon materials are still rare. Searching for such materials with salient physics has become a new direction for carbon research. Here, using first-principles calculations and tight-binding modeling, we study three types of 3D graphene networks whose properties inherit those of Dirac electrons in graphene. In the band structures of these materials, two flat Weyl surfaces appear in the Brillouin zone (BZ), which straddle the Fermi level and are robust against external strain. When the networks are cut, the resulting lower-dimensional slabs and nanowires remain to be semimetallic with Weyl line-like and point-like Fermi surfaces, respectively. Between the Weyl lines, flat surface bands emerge with strong magnetism when each surface carbon atom is passivated by one hydrogen atom. The robustness of these structures can be traced back to a bulk topological invariant, ensured by the sublattice symmetry, and to the one-dimensional (1D) Weyl semimetal behavior of the zigzag carbon chain, which has been the common backbone to all these structures. The flat Weyl-surface semimetals may enable applications in correlated electronics, as well as in energy storage, molecular sieve, and catalysis because of their good stability, porous geometry, and large superficial area.