arXiv subjects

Isao Tomita

Publications and source records attributed to Isao Tomita.

4 recordsLinked to original sources

arXiv2019

Electronic and structural properties of 3D Hopf-linked carbon allotrope: Hopfene

Electronic and structural properties of a 3D carbon allotrope made of Hopf-linked graphenes, which we call a Hopfene - a type of topological crystal, are examined by semi-empirical molecular-orbital and density-functional-theoretical methods, where band-structure analyses reveal very different properties from those of 2D graphenes. Furthermore, the analyses give an interesting finding that, depending on graphene-sheet spacings, Hopfenes exhibit different band features between primary-type Hopfene with a finite minimum sheet spacing and secondary type with its double-sized spacing. The primary type shows semi-metallic nature and the secondary type exhibits semi-metallic or semiconducting nature at different bands and also has flat bands; these conducting features can be utilised by Fermi-level control. A device application of Hopfenes is also provided.

cond-mat.mtrl-sci↗

arXiv2019

Lattice deformation on flat-band modulation in 3D Hopf-linked carbon allotrope: Hopfene

Flat bands form in a 3D Hopf-linked graphene crystal or a 3D carbon allotrope named Hopfene, which qualitatively differ from bands of only graphenes. This paper discusses carbon-hexagon deformation on the level shift of a flat band via density-functional-theoretical (DFT) analysis to set the flat-band level to the Fermi level, viz., to utilize its large density of states for magnetic- and electronic-property researches. Tight-binding (TB) analysis is also performed for a comparison with the DFT analysis; here, a qualitative agreement between TB and DFT bands is obtained. The DFT analysis shows an almost linear flat-band level shift to the lattice-deformation rate, where electron-interaction effects are included within the Kohn-Sham method. To tune the flat-band level so that it fits the Fermi level, a double-hetero-like structure is also proposed as a way of hexagon-deformation control.

cond-mat.mtrl-sci↗

arXiv2019

Topological carbon allotropes: paradigm shift for materials innovation

Topology is a central concept of mathematics, which allows us to distinguish two isolated rings with linked ones. In material science, researchers discovered topologically different carbon allotropes in a form of a cage, a tube, and a sheet, which have unique translational and rotational symmetries, described by a crystallographic group theory, and the atoms are arranged at specific rigid positions in 3-dimensional ($D$) space. However, topological orders must be robust against deformations, so that we can make completely different families of topological materials. Here we propose various topological structures such as knots and links using covalent $σ$ bonds of carbon atoms, while allowing various topologically equivalent arrangements using weak $π$ bonds. By extending this idea, we invented a new 3D carbon allotrope, Hopfene, which has periodic arrays of Hopf-links to knit horizontal Graphene sheets into vertical ones without connecting by $σ$ bonds.

cond-mat.mes-hall↗

arXiv2019

Dirac and Weyl Fermions in 3D Hopf-linked Honeycomb Lattices: Hopfene

Carbon allotropes such as diamond, nano-tube, Fullerene, and Graphene, have unique lattice symmetries of crystal lattice, but these are topologically trivial. We have proposed a topologically-nontrivial allotrope, named Hopfene, which has three-dimensional (3D) arrays of Hopf-links to bind 2D Graphene sheets both vertically and horizontally. Here, we describe the electronic structures of Hopfene by simple tight-binding calculations. We confirmed the original Dirac points of 2D Graphene were topologically protected upon the introduction of the Hopf links, and low-energy excitations are described by 1D, 2D, and 3D Dirac and Weyl Fermions.

cond-mat.mes-hall↗