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

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

Transverse field effect in graphene ribbons

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

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

The effect of the patterning process on the nonlinearity of the microwave surface resistance $R_S$ of YBCO thin films is investigated. With the use of a sapphire dielectric resonator and a stripline resonator, the microwave $R_S$ 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 $J_{rf}^2$ dependence of $Z_S(J_{rf})$ on current density $J_{rf}$. Experimental and modeled results show that the patterning has no observable effect on the microwave residual $R_S$ or on the power dependence of $R_S$.Comment: Submitted to IEEE Trans. MT

Universal Features of Quantized Thermal Conductance of Carbon Nanotubes

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

Peculiar Width Dependence of the Electronic Property of Carbon Nanoribbons

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 $w$ in terms of $p$ and $q$. 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 $w$. We reveal a peculiar dependence of the electronic property of nanoribbons on the width $w$.Comment: 8 pages, 13 figure

High field electro-thermal transport in metallic carbon nanotubes

We describe the electro-thermal transport in metallic carbon nanotubes (m-CNTs) by a semi-classical approach that takes into account the high-field dynamical interdependence between charge carrier and phonon populations. Our model is based on the self-consistent solution of the Boltzmann transport equation and the heat equation mediated by a phonon rate equation that accounts for the onset of non-equilibrium (optical) phonons in the high-field regime. Given the metallic nature of the nanostructures, a key ingredient of the model is the assumption of local thermalization of charge carriers. Our theory remarkably reproduces the room temperature electrical characteristics of m-CNTs on substrate and free standing (suspended), shedding light on charge-heat transport in these one dimensional nanostructures. In particular, the negative differential resistance observed in suspended m-CNTs under electric stress is attributed to inhomogeneous field profile induced by self-heating rather than the presence of hot phonons.Comment: 10 pages, 10 figure

Phase Diagrams of Bi1-xSbx Thin Films with Different Growth Orientations

A closed-form model is developed to evaluate the band-edge shift caused by quantum confinement for a two-dimensional non-parabolic carrier-pocket. Based on this model, the symmetries and the band-shifts of different carrier-pockets are evaluated for BiSb thin films that are grown along different crystalline axes. The phase diagrams for the BiSb thin film systems with different growth orientations are calculated and analyzed