Chengyong Zhong — Page 2

arXiv2016

Coexistence of flat bands and Dirac bands in a carbon-Kagome-lattice family

The Dirac bands and flat bands are difficult to coexist because they represent two extreme ends of electronic properties. However, in this paper, we propose a carbon-Kagome-lattice (CKL) family based on first-principles calculations, and the coexistence of Dirac and flat bands are observed in this series of three-dimensional carbon structures. The flat bands are originated from the orbital interactions of the Kagome lattices, while the Dirac bands are related to the carbon zigzag chains. A tight-binding model is used to explain the various band structures in different CKLs. The coexistence of flat and Dirac bands around the Fermi level implies that CKL structures maybe can serve as superconductors. In addition, electronic properties of the thinnest CKL slabs, only consisting of benzene rings, are studied. Flat bands are found in the band spectra of the two-dimensional structures, and split into spin-up and spin-down bands because of strong correlated effect in the case of hole doping.

cond-mat.mtrl-sci↗

arXiv2016

Towards Three-Dimensional Weyl-SurfaceSemimetals in Graphene Networks

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.

cond-mat.mtrl-sci↗