Eigenmode in a misaligned triangular optical cavity

We derive relationships between various types of small misalignments on a triangular Fabry-Perot cavity and associated geometrical eigenmode changes. We focus on the changes of beam spot positions on cavity mirrors, the beam waist position, and its angle. A comparison of analytical and numerical results shows excellent agreement. The results are applicable to any triangular cavity close to an isosceles triangle, with the lengths of two sides much bigger than the other, consisting of a curved mirror and two flat mirrors yielding a waist equally separated from the two flat mirrors. This cavity shape is most commonly used in laser interferometry. The analysis presented here can easily be extended to more generic cavity shapes. The geometrical analysis not only serves as a method of checking a simulation result, but also gives an intuitive and handy tool to visualize the eigenmode of a misaligned triangular cavity.Comment: 17 pages, 21 figure

Local Energy Gap in Deformed Carbon Nanotubes

The effects of graphite surface geometrical deformation on the dynamics of conducting electrons are investigated theoretically. The analysis is performed within the framework of a deformation-induced gauge field and corresponding deformation-induced magnetic field. It is shown that the latter gives a local energy gap along the axis of a deformed nanotube. We compare our energy gap results with experimental data on energy gaps in nanotubes and peapods. We also discuss the mixing of two Fermi points and construct a general model of low energy dynamics, including a short-range deformation of the graphite sheet. This model is equivalent to the Weyl equation in {\it U}(1) Abelian and {\it SU}(2) non-Abelian deformation-induced gauge fields.Comment: 18 pages, 4 figures, corrected typos, added references, improved presentation (v4, published version

First-principles study of phenyl ethylene oligomers as current-switch

We use a self-consistent method to study the distinct current-switch of $2^{'}$-amino-4-ethynylphenyl-4'-ethynylphenyl-5'-nitro-1-benzenethiol, from the first-principles calculations. The numerical results are in accord with the early experiment [Reed et al., Sci. Am. \textbf{282}, 86 (2000)]. To further investigate the transport mechanism, we calculate the switching behavior of p-terphenyl with the rotations of the middle ring as well. We also study the effect of hydrogen atom substituting one ending sulfur atom on the transport and find that the asymmetry of I-V curves appears and the switch effect still lies in both the positive and negative bias range.Comment: 6 pages, 6 figure

Controlling edge states of zigzag carbon nanotubes by the Aharonov-Bohm flux

It has been known theoretically that localized states exist around zigzag edges of a graphite ribbon and of a carbon nanotube, whose energy eigenvalues are located between conduction and valence bands. We found that in metallic single-walled zigzag carbon nanotubes two of the localized states become critical, and that their localization length is sensitive to the mean curvature of a tube and can be controlled by the Aharonov-Bohm flux. The curvature induced mini-gap closes by the relatively weak magnetic field. Conductance measurement in the presence of the Aharonov-Bohm flux can give information about the curvature effect and the critical states.Comment: 5 pages, 4 figure

Aharonov-Bohm effect in higher genus materials

Flux periodicity of conducting electrons on a closed surface with genus two $g=2$ (double torus) are investigated theoretically. We examine flux periodicity of the ground-state energy and of the wave functions as a function of applied magnetic field. A fundamental flux period of the ground-state energy is twice a fundamental unit of magnetic flux for uniformly applied magnetic field, which is shown to be valid for a simple ladder geometry and carbon double torus. Flux periodicity of the wave functions in a double torus is complicate as compared with a simple torus ($g=1$), and an adiabatic addition of magnetic fluxes does not provide a good quantum number for the energy eigenstates. The results are extended to higher genus materials and the implications of the results are discussed.Comment: 4 pages, 6 figure

Polarization Induced Switching Effect in Graphene Nanoribbon Edge-Defect Junction

With nonequilibrium Green's function approach combined with density functional theory, we perform an ab initio calculation to investigate transport properties of graphene nanoribbon junctions self-consistently. Tight-binding approximation is applied to model the zigzag graphene nanoribbon (ZGNR) electrodes, and its validity is confirmed by comparison with GAUSSIAN03 PBC calculation of the same system. The origin of abnormal jump points usually appearing in the transmission spectrum is explained with the detailed tight-binding ZGNR band structure. Transport property of an edge defect ZGNR junction is investigated, and the tunable tunneling current can be sensitively controlled by transverse electric fields.Comment: 18 pages, 8 figure