3,345 research outputs found

    Transverse field effect in graphene ribbons

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    It is shown that a graphene ribbon, a ballistic strip of carbon monolayer, may serve as a quantum wire whose electronic properties can be continuously and reversibly controlled by an externally applied transverse voltage. The electron bands of armchair-edge ribbons undergo dramatic transformations: The Fermi surface fractures, Fermi velocity and effective mass change sign, and excitation gaps are reduced by the transverse field. These effects are manifest in the conductance plateaus, van Hove singularities, thermopower, and activated transport. The control over one-dimensional bands may help enhance effects of electron correlations, and be utilized in device applications.Comment: 4 pages, 3 figure

    Transition from a Tomonaga-Luttinger liquid to a Fermi liquid in potassium intercalated bundles of single wall carbon nanotubes

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    We report on the first direct observation of a transition from a Tomonaga-Luttinger liquid to a Fermi liquid behavior in potassium intercalated mats of single wall carbon nanotubes (SWCNT). Using high resolution photoemission spectroscopy an analysis of the spectral shape near the Fermi level reveals a Tomonaga-Luttinger liquid power law scaling in the density of states for the pristine sample and for low dopant concentration. As soon as the doping is high enough to fill bands of the semiconducting tubes a distinct transition to a bundle of only metallic SWCNT with a scaling behavior of a normal Fermi liquid occurs. This can be explained by a strong screening of the Coulomb interaction between charge carriers and/or an increased hopping matrix element between the tubes.Comment: 5 pages, 4 figure

    Universal Features of Quantized Thermal Conductance of Carbon Nanotubes

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    The universal features of quantized thermal conductance of carbon nanotubes (CNTs) are revealed through theoretical analysis based on the Landauer theory of heat transport. The phonon-derived thermal conductance of semiconducting CNTs exhibits a universal quantization in the low temperature limit, independent of the radius or atomic geometry. The temperature dependence follows a single curve given in terms of temperature scaled by the phonon energy gap. The thermal conductance of metallic CNTs has an additional contribution from electronic states, which also exhibits quantized behavior up to room temperature.Comment: 4 pages, 5 figures. accepted for publication in Phys. Rev. Let

    Comparison of Power Dependence of Microwave Surface Resistance of Unpatterned and Patterned YBCO Thin Film

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    The effect of the patterning process on the nonlinearity of the microwave surface resistance RSR_S of YBCO thin films is investigated. With the use of a sapphire dielectric resonator and a stripline resonator, the microwave RSR_S of YBCO thin films was measured before and after the patterning process, as a function of temperature and the rf peak magnetic field in the film. The microwave loss was also modeled, assuming a Jrf2J_{rf}^2 dependence of ZS(Jrf)Z_S(J_{rf}) on current density JrfJ_{rf}. Experimental and modeled results show that the patterning has no observable effect on the microwave residual RSR_S or on the power dependence of RSR_S.Comment: Submitted to IEEE Trans. MT

    Science of fullerenes and carbon nanotubes

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    Peculiar Width Dependence of the Electronic Property of Carbon Nanoribbons

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    Nanoribbons (nanographite ribbons) are carbon systems analogous to carbon nanotubes. We characterize a wide class of nanoribbons by a set of two integers , and then define the width ww in terms of pp and qq. Electronic properties are explored for this class of nanoribbons. Zigzag (armchair) nanoribbons have similar electronic properties to armchair (zigzag) nanotubes. The band gap structure of nanoribbons exhibits a valley structure with stream-like sequences of metallic or almost metallic nanoribbons. These sequences correspond to equi-width curves indexed by ww. We reveal a peculiar dependence of the electronic property of nanoribbons on the width ww.Comment: 8 pages, 13 figure

    Disorder-induced superconductivity in ropes of carbon nanotubes

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    We study the interplay between disorder and superconductivity in a rope of metallic carbon nanotubes. Based on the time dependent Ginzburg Landau theory, we derive the superconducting transition temperature Tc_c taking into account the critical superconducting fluctuations which are expected to be substantially strong in such low dimensional systems. Our results indicate that, contrary to what is expected, Tc_c increases by increasing the amount of disorder. We argue that this behavior is due to the dynamics of the tubes which reduces the drastic effect of the local disorder on superconductivity by enhancing the intertube Josephson tunneling. We also found that Tc_c is enhanced as the effective dimensionality of the rope increases by increasing the number N of the tubes forming the rope. However, Tc_c tends to saturate for large values of N, expressing the establishment of a bulk three dimensional (3D) superconducting order.Comment: 9 pages, 4 figur

    Radiation damage annealing kinetics in lithium-diffused silicon solar cells

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    Development of computer program to predict performance from specified cell characteristics in lithium-diffused silicon solar cell
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