Observation of Enhanced Beaming from Photonic Crystal Waveguides

We report on the experimental observation of the beaming effect in photonic crystals enhanced via surface modes. We experimentally map the spatial field distribution of energy emitted from a subwavelength photonic crystal waveguide into free-space, rendering with crisp clarity the diffractionless beaming of energy. Our experimental data agree well with our numerical studies of the beaming enhancement in photonic crystals with modulated surfaces. Without loss of generality, we study the beaming effect in a photonic crystal scaled to microwave frequencies and demonstrate the technological capacity to deliver long-range, wavelength-scaled beaming of energy.Comment: 4 pages, 6 figure

Geometrical structure effect on localization length of carbon nanotubes

The localization length and density of states of carbon nanotubes are evaluated within the tight-binding approximation. By comparison with the corresponding results for the square lattice tubes, it is found that the hexagonal structure affects strongly the behaviors of the density of states and localization lengths of carbon nanotubes.Comment: 7 pages, 4 figures, revised version to appear in Chin. Phys. Lett. The title is changed. Some arguments are adde

Disclination vortices in elastic media

The vortex-like solutions are studied in the framework of the gauge model of disclinations in elastic continuum. A complete set of model equations with disclination driven dislocations taken into account is considered. Within the linear approximation an exact solution for a low-angle wedge disclination is found to be independent from the coupling constants of the theory. As a result, no additional dimensional characteristics (like the core radius of the defect) are involved. The situation changes drastically for 2\pi vortices where two characteristic lengths, l_\phi and l_W, become of importance. The asymptotical behaviour of the solutions for both singular and nonsingular 2\pi vortices is studied. Forces between pairs of vortices are calculated.Comment: 13 pages, published versio

Suppression of electron-electron repulsion and superconductivity in Ultra Small Carbon Nanotubes

Recently, ultra-small-diameter Single Wall Nano Tubes with diameter of $\sim 0.4 nm$ have been produced and many unusual properties were observed, such as superconductivity, leading to a transition temperature $T_c\sim 15^oK$, much larger than that observed in the bundles of larger diameter tubes. By a comparison between two different approaches, we discuss the issue whether a superconducting behavior in these carbon nanotubes can arise by a purely electronic mechanism. The first approach is based on the Luttinger Model while the second one, which emphasizes the role of the lattice and short range interaction, is developed starting from the Hubbard Hamiltonian. By using the latter model we predict a transition temperature of the same order of magnitude as the measured one.Comment: 7 pages, 3 figures, to appear in J. Phys.-Cond. Ma

Size Effects in Carbon Nanotubes

The inter-shell spacing of multi-walled carbon nanotubes was determined by analyzing the high resolution transmission electron microscopy images of these nanotubes. For the nanotubes that were studied, the inter-shell spacing ${\hat{d}_{002}}$ is found to range from 0.34 to 0.39 nm, increasing with decreasing tube diameter. A model based on the results from real space image analysis is used to explain the variation in inter-shell spacings obtained from reciprocal space periodicity analysis. The increase in inter-shell spacing with decreased nanotube diameter is attributed to the high curvature, resulting in an increased repulsive force, associated with the decreased diameter of the nanotube shells.Comment: 4 pages. RevTeX. 4 figure

Theory of extraordinary optical transmission through subwavelength hole arrays

We present a fully three-dimensional theoretical study of the extraordinary transmission of light through subwavelength hole arrays in optically thick metal films. Good agreement is obtained with experimental data. An analytical minimal model is also developed, which conclusively shows that the enhancement of transmission is due to tunneling through surface plasmons formed on each metal-dielectric interfaces. Different regimes of tunneling (resonant through a ''surface plasmon molecule", or sequential through two isolated surface plasmons) are found depending on the geometrical parameters defining the system.Comment: 4 pages, 4 figure

Effective low-energy theory for correlated carbon nanotubes

The low-energy theory for single-wall carbon nanotubes including Coulomb interactions is derived and analyzed. It describes two fermion chains without interchain hopping but coupled in a specific way by the interaction. The strong-coupling properties are studied by bosonization, and consequences for experiments on single armchair nanotubes are discussed.Comment: 5 pages REVTeX, includes one figur

Band structures of periodic carbon nanotube junctions and their symmetries analyzed by the effective mass approximation

The band structures of the periodic nanotube junctions are investigated by the effective mass theory and the tight binding model. The periodic junctions are constructed by introducing pairs of a pentagonal defect and a heptagonal defect periodically in the carbon nanotube. We treat the periodic junctions whose unit cell is composed by two kinds of metallic nanotubes with almost same radii, the ratio of which is between 0.7 and 1 . The discussed energy region is near the undoped Fermi level where the channel number is kept to two, so there are two bands. The energy bands are expressed with closed analytical forms by the effective mass theory with some assumptions, and they coincide well with the numerical results by the tight binding model. Differences between the two methods are also discussed. Origin of correspondence between the band structures and the phason pattern discussed in Phys. Rev. B {\bf 53}, 2114, is clarified. The width of the gap and the band are in inverse proportion to the length of the unit cell, which is the sum of the lengths measured along the tube axis in each tube part and along 'radial' direction in the junction part. The degeneracy and repulsion between the two bands are determined only from symmetries.Comment: RevTeX, gif fil

Strong coupling between surface plasmon-polaritons and organic molecules in subwavelength hole arrays

J. Dintinger, S. Klein, F. Bustos, William L. Barnes, and T. W. Ebbesen, Physical Review B, Vol. 71, article 035424 (2005). "Copyright © 2005 by the American Physical Society."The interaction of a J-aggregate and surface plasmon polariton modes of a subwavelength hole array have been studied in detail. By measuring the effects of hole array period, angular dispersion and concentration of the J-aggregate on the transmission of the array, the existence of a strong coupling regime is demonstrated with a Rabi splitting of 250 meV. This large splitting is explained not only by the high oscillator strength of the dye but also by the high local field amplitudes generated by surface plasmons of the metallic structure