Effect of spin-orbit coupling on zero-conductance resonances in asymmetrically coupled one-dimensional rings

The influence of Rashba spin-orbit coupling on zero conductance resonances appearing in one dimensional ring asymmetrically coupled to two leads is investigated. For this purpose, the transmission function of the corresponding one-electron scattering problem is derived analytically and analyzed in the complex energy plane with focus on the zero-pole structure characteristic of transmission (anti)resonances. The lifting of real conductance zeros due to spin-orbit coupling in the asymmetric Aharonov-Casher (AC) ring is related to the breaking of spin reversal symmetry in analogy to the time-reversal symmetry breaking in the asymmetric Aharonov-Bohm (AB) ring.Comment: 10 pages, 11 figure

Numerical study of the lattice vacancy effects on the single-channel electron transport of graphite ribbons

Lattice vacancy effects on electrical conductance of nanographite ribbon are investigated by means of the Landauer approach using a tight binding model. In the low-energy regime ribbons with zigzag boundary provide a single conducting channel whose origin is connected with the presence of edge states. It is found that the chemical potential dependence of conductance strongly depends on the difference ($\Delta$) of the number of removed A and B sublattice sites. The large lattice vacancy with $\Delta\neq 0$ shows $2\Delta$ zero-conductance dips in the single-channel region, however, the large lattice vacancy with $\Delta=0$ has no dip structure in this region. The connection between this conductance rule and the Longuet-Higgins conjecture is also discussed

Magnetic Structure of Nano-Graphite Moebius Ribbon

We consider the electronic and magnetic properties of nanographite ribbon with zigzag edges under the periodic or Moebius boundary conditions. The zigzag nano-graphite ribbons possess edge localized states at the Fermi level which cause a ferrimagnetic spin polarization localized at the edge sites even in the very weak Coulomb interaction. The imposition of the Moebius boundary condition makes the system non-AB-bipartite lattice, and depress the spin polarization, resulting in the formation of a magnetic domain wall. The width of the magnetic domain depends on the Coulomb interaction and narrows with increasing U/t.Comment: 4 pages; 6 figures; published at J. Phys. Soc. Jpn. Vol. 72 No. 5 pp. 998-1001 (2003

Competition between spin and charge polarized states in nanographene ribbons with zigzag edges

Effects of the nearest neighbor Coulomb interaction on nanographene ribbons with zigzag edges are investigated using the extended Hubbard model within the unrestricted Hartree-Fock approximation. The nearest Coulomb interaction stabilizes a novel electronic state with the opposite electric charges separated and localized along both edges, resulting in a finite electric dipole moment pointing from one edge to the other. This charge-polarized state competes with the peculiar spin-polarized state caused by the on-site Coulomb interaction and is stabilized by an external electric field.Comment: 4 pages; 4 figures; accepted for publication in Phys. Rev. B; related Web site: http://staff.aist.go.jp/k.harigaya/index_E.htm

Resonant X-ray Study on the Bi-Layered Perovskite Mn Oxide LaSr2Mn2O7

Charge and orbital ordering behaviors in the half doped bi-layered compound LaSr2Mn2O7 have been studied by resonant and non-resonant X-ray scattering. Three different order parameters, which correspond to the A-type antiferromagnetic, a charge and an orbital ordered states, were observed by measuring the magnetostriction and the superlattice peaks characterized by wavevectors (1/2 1/2 0) and (1/4 1/4 0), respectively. The superlattice reflections indicating the charge and orbital ordered states were observed below 210 K. Both the intensities reach a maximum at 160 K on cooling and become very weak below 100 K. The peak width of the charge ordered state agrees with that of the orbital ordered state at all temperatures studied. These results indicate that both the states originate from a single phase and that the charge/orbital ordered islands with definite interfaces disperse in the A-type antiferromagnetic phase. The dimensionality of the charge/orbital ordered phase is discussed using this model.Comment: 9pages, 10 figure

Soliton Trap in Strained Graphene Nanoribbons

The wavefunction of a massless fermion consists of two chiralities, left-handed and right-handed, which are eigenstates of the chiral operator. The theory of weak interactions of elementally particle physics is not symmetric about the two chiralities, and such a symmetry breaking theory is referred to as a chiral gauge theory. The chiral gauge theory can be applied to the massless Dirac particles of graphene. In this paper we show within the framework of the chiral gauge theory for graphene that a topological soliton exists near the boundary of a graphene nanoribbon in the presence of a strain. This soliton is a zero-energy state connecting two chiralities and is an elementally excitation transporting a pseudospin. The soliton should be observable by means of a scanning tunneling microscopy experiment.Comment: 7 pages, 4 figure

Correlation effects of carbon nanotubes at boundaries: Spin polarization induced by zero-energy boundary states

When a carbon nanotube is truncated with a certain type of edges, boundary states localized near the edges appear at the fermi level. Starting from lattice models, low energy effective theories are constructed which describe electron correlation effects on the boundary states. We then focus on a thin metallic carbon nanotube which supports one or two boundary states, and discuss physical consequences of the interaction between the boundary states and bulk collective excitations. By the renormalization group analyses together with the open boundary bosonization, we show that the repulsive bulk interactions suppress the charge fluctuations at boundaries, and assist the spin polarization.Comment: 8 pages, 1 figur

A New Endoscopic Technique for Examination of Esophageal Stenosis: The Funnel-shaped Transparent Cap Technique

We have devised a funnel-shaped transparent cap for the endoscopic diagnosis and treatment of stenosis in the digestive tract. This funnel-shaped cap is made of highly transparent methacrylic resin. A 73-year-old woman with reflux esophagitis (categorized as grade D by the Los Angeles Classification) visited our hospital with the chief complaint of dysphagia. She was examined using an endoscope equipped with a transparent vinyl chloride hood at its tip. Many pieces of food were found to be trapped in the esophagus. These were removed using tripod forceps or aspirated into the hood. The internal diameter of the stenotic segment was as small as 1 or 2 mm, and it was difficult to advance the endoscope past the stenosis. The endoscope was withdrawn, and the attached hood was removed and replaced with a transparent cap. This provided clear visualization of the mucosal surface of the stenotic segment, which could not be examined using any conventional device, permitting the stenosis to be relieved