Masatsura Igami

Lattice Distortion in Nanographite Ribbons

We study the lattice distortion in graphite ribbons of a nanometer width by taking account of the electron-phonon interaction in the tight binding model. In the ribbons with armchair edges, the typical Kekule structure appears near the edges depending on the distribution of the bond orders. On the other hand, the zigzag ribbons do not undergo bond alternations along the ribbon axis, implying less Peierls instability. Special emphasis is put on the survival of the edge state which forms almost flat bands and a sharp peak in the density of states in consideration of the electron-phonon interaction.

Conductance of carbon nanotubes with a vacancy

The conductance of carbon nanotubes with a vacancy is studied in a tight-binding model. We examine the Fermi energy e dependence of the conductance and show it is quantized into zero, one, and two times the conductance quantum \(e^{2}/\pi\hbar\) depending on the type of vacancy in the half-filled case, i.e., e= 0. In the presence of a magnetic field, the conductance is scaled by the component of the magnetic field in the direction of the vacancy.

Effective-Mass Theory of Carbon Nanotubes with Vacancy

Effects of impurities with a strong and short-range potential are studied in carbon nanotubes within a k · p scheme. The calculated conductance approaches those obtained for nanotubes with a lattice vacancy when the strength of the potential is sufficiently large. The conductance at e=0 is analytically shown to be quantized into zero, one, and two times of the conductance quantum \(e^2/\pi\hbar\) depending on the difference in the number of vacancies at A and B sublattices in nanotubes with a sufficiently large diameter.

Numerical Study of Transport in Carbon Nanotubes with Lattice Vacancy

The conductance is calculated for approximately 1.6×10 5 armchair carbon nanotubes (CNs) with a different lattice vacancy in a tight-binding model using a multi-channel Landauers formula. When th...

Phonon dispersion of nano-graphite ribbons

Based on the classical force constant models, we study numerically and analytically out-of-plane phonon-dispersion relations for two types of nano-graphite ribbons confined by the armchair- and zigzag-shaped edges. We demonstrate for two ribbons how the edge-localized vibrational modes, i.e., edge phonon modes, behave depending on edge environment by means of altering the effective mass of the edge sites. Special emphasis is placed on the qualitative difference in the phonon modes which are localized near two types of edges.

Electron-Electron Interaction in Nanographite Ribbons

We study the π electronic structure of graphite ribbons of a nanometer width by taking account of the long-range electron-electron interaction. The primary features like energy dispersion and bond order distribution are essentially determined by the nearest-neighbor transfer alone, meaning their strong dependency on the connectivity relation in the π electron network. The Coulomb interaction, on the other hand, is induced by the sites of longer distances as well, which means that the Coulomb repulsion reflects the site geometry in the atomic configuration. We focus on the geometry-dependent Coulomb interaction and discuss how it influences the electronic state near the Fermi level which is governed by the network topology. The Coulomb repulsion under the geometry of armchair ribbons works against the bond order distribution determined by the network topology. This may lead to a frustrated system especially for a quite narrow ribbon. The Coulomb interaction in zigzag ribbons tends to open a gap with/withou...

Electronic and geometric structures of fluorine adsorbed graphene

We study electronic and geometric structures of the fluorine adsorbed graphene sheet using an ab initio pseudopotential method. We find that the fluorine atom forms covalent bond with the carbon atom and locally terminates the π-states on the graphene sheet. The charge distribution exhibits a typical √3 x √3 structure near the Fermi energy. This means that the doped fluorine atom acts as a local defect on the π-electron network of a graphene sheet.

Magnetism of nanometer-scale graphite with edge or topological defects

Abstract Magnetic structure is studied for several π-networks of graphite-like structures with edge and/or topological defects using the tight-binding model (the Huckel model). Zigzag-edged graphite have edge states, which form a partly flat band at the Fermi energy. Short range repulsion (the Hubbard U) is enough to induce huge magnetic moments coming from spin polarization of localized electrons on the edge. While, introduction of azupyrene defect (two pentagons and two heptagons instead of four hexagons) in graphite modifies the band structure, some of which have a flat lowest excitation band. We propose a series of one-dimensional polymers with a flat band, which is exactly shown to be ferromagnetic for electron doping up to the half-filling of this band, so long as the system is well described by the Hubbard model.

Effective Mass Theory of Carbon Nanotubes with Vacancies in Magnetic Fields.

An effective-mass theory is developed on transport of non-doped carbon nanotubes with local and short-range impurities in the presence of a magnetic field. The conductance is shown to be scaled com...

Effect of lattice vacancy on conductance of carbon nanotubes

Conductance of carbon nanotubes with a lattice vacancy in the presence or absence of a magnetic field is studied within a tight-binding model. In the absence of a magnetic field, it is quantized into zero, one, or two times of e2/πℏ depending on the type of the vacancy if its size is much smaller than the circumference. This strong dependence on kinds of vacancies prevails even in a magnetic field perpendicular to the axis.