Electronic Properties of Topological Materials: Optical Excitations in Moebius Conjugated Polymers

Electronic structures and optical excitations in Moebius conjugated polymers are studied theoretically. Periodic and Moebius boundary conditions are applied to the tight binding model of poly(para-phenylene), taking exciton effects into account. We discuss that oligomers with a few structural units are more effective than polymers for observations of effects of discrete wave numbers that are shifted by the change in boundary condition. Next, calculations of optical absorption spectra are reported. Certain components of optical absorption for an electric field perpendicular to the polymer axis mix with absorption spectra for an electric field parallel to the polymer axis. Therefore, the polarization dependences of an electric field of light enable us to detect whether conjugated polymers have the Moebius boundary.Comment: 10 pages, 6 figures, to be published in J. Phys. Soc. Jpn., Vol. 74 No. 2 (February, 2005), Letter sectio

Room-temperature ballistic transport in narrow graphene strips

We investigate electron-phonon couplings, scattering rates, and mean free paths in zigzag-edge graphene strips with widths of the order of 10 nm. Our calculations for these graphene nanostrips show both the expected similarity with single-wall carbon nanotubes (SWNTs) and the suppression of the electron-phonon scattering due to a Dirichlet boundary condition that prohibits one major backscattering channel present in SWNTs. Low-energy acoustic phonon scattering is exponentially small at room temperature due to the large phonon wave vector required for backscattering. We find within our model that the electron-phonon mean free path is proportional to the width of the nanostrip and is approximately 70 $\mu$m for an 11-nm-wide nanostrip.Comment: 5 pages and 5 figure

Theory of Spin polarized Tunneling in Superconducting Sr2RuO4

A theory of tunneling conductance in ferromagnetic metal/insulator/triplet - supercondcutor junctions is presented for unitary and non-unitary spin triplet pairing states which are promising candidates for the superconducting paring symmetry of Sr2RuO4. As the magnitude of the exchange interaction in the ferromagnetic metal is increased, the conductance for the unitary pairing state below the energy gap is reduced in contrast to the case for the non-unitary pairing state

Ferromagnetic features on zero-bias conductance peaks in ferromagnet/insulator/superconductor junction

We present a formula for tunneling conductance in ballistic ferromagnet/ferromagnetic insulator/superconductor junctions where the superconducting state has opposite spin pairing symmetry. The formula can involve correctly a ferromagnetism has been induced by effective mass difference between up- and down-spin electrons. Then, this effective mass mismatch ferromagnet and standard Stoner ferromagnet have been employed in this paper. As an application of the formulation, we have studied the tunneling effect for junctions including spin-triplet p-wave superconductor. The conductace spectra show a clear difference between two ferromagnets depending upon the way of normalization of the conductance. Especially, a essential difference is seen in zero-bias conductance peaks reflecting characteristics of each ferromagnets. From obtained results, it will be suggested that the measurements of the tunneling conductance in the junction provide us a useful information about the mechanism of itinerant ferromagnetism in metal.Comment: 8 pages, 8 figures, references added to the first versio

Tunneling current in triplet f-wave superconductors with horizontal lines of nodes

We calculate the tunneling conductance spectra of a normal-metal/insulator/triplet superconductor using the Blonder-Tinkham-Klapwijk (BTK) formulation. Possible states for the superconductor are considered with horizontal lines of nodes, breaking the time reversal symmetry. These results would be useful to discriminate between pairing states in superonductor Sr$_2$RuO$_4$ and also in UPt$_3$.Comment: 12 pages, 7 figure

Variación latitudinal del ciclo reproductivo de dos bivalvos con orígenes biogeográficos contrastantes a lo largo del ecosistema de afloramiento de la Corriente de Humboldt

Argopecten purpuratus (Lamarck, 1819) and Mesodesma donacium (Lamarck, 1818) are bivalves that inhabit the Humboldt Current Upwelling Ecosystem. They have contrasting biogeographical origins, suggesting that their responses to exogenous factors should differ. Using circular statistics, we examine synchrony/asynchrony in the reproductive cycle between populations of each species. The results indicate that there is reproductive asynchrony in both species along their distributional range. However, there was synchrony for A. purpuratus in several location-pairs, including Paita-Chimbote, Chimbote-Callao, Callao-Pisco and Pisco-Antofagasta. For M. donacium, there were only two synchronic groups: Camaná-Capellanía-Mehuín and Hornitos-Peñuelas-Longotoma-La Ligua-Cucao-Quilanlar. A. purpuratus showed gametogenenic activity throughout the year. In contrast, M. donacium showed strong seasonality, with gametogenesis in winter and spawning in spring/summer. In conclusion, the patterns observed for these sympatric species suggest that on a large scale the reproductive cycles follow the expected patterns for the contrasting biogeographic origin of each species, so it could be argued that they are modulated by endogenous factors. However, at a local scale, the reproductive cycles of these species show variation, likely determined by local oceanographic or hydrographic processes.Argopecten purpuratus (Lamarck, 1819) y Mesodesma donacium (Lamarck, 1818) son moluscos bivalvos endémicos del sistema de afloramiento de la Corriente de Humboldt pero tienen orígenes biogeográficos opuestos. Por tanto, se esperaría que los factores exógenos afectaran sus ritmos biológicos diferencialmente, entre ellos sus ciclos reproductivos. Mediante análisis de distribución circular se evaluó el sincronismo/asincronismo en ciclos reproductivos entre poblaciones de cada especie. Los resultados indican que existe asincronía reproductiva en ambas especies a lo largo de su distribución. Sin embargo para A. purpuratus se encontró varios pares de localidades sincrónicas: Paita-Chimbote; Chimbote-Callao; Callao-Pisco y Pisco-Antofagasta, y para M. donacium se dieron dos grupos sincrónicos, el primero entre las poblaciones de Camaná, Capellanía y Mehuín; y el segundo grupo entre Hornitos, Peñuelas, Longotoma, La Ligua, Cucao y Quilanlar. A. purpuratus presentó actividad gametogénica continua. En contraste, M. donacium presentó una marcada estacionalidad, con gametogénesis durante invierno y desoves durante primavera y/o verano. En conclusión, los patrones observados para ambas especies simpátricas sugieren que, a gran escala el ciclo reproductivo sigue los patrones esperados para el origen biogeográfico contrastante de cada especie, por lo tanto se podría argumentar que es modulada por factores endógenos. Sin embargo, a escala local el ciclo reproductivo de ambas especies muestra variaciones, aparentemente influenciados por los factores oceanográficos o hidrográficos locales