Magnetoasymmetric transport in a mesoscopic interferometer: From the weak to the strong coupling regime

The microreversibility principle implies that the conductance of a two-terminal Aharonov-Bohm interferometer is an even function of the applied magnetic flux. Away from linear response, however, this symmetry is not fulfilled and the conductance phase of the interferometer when a quantum dot is inserted in one of its arms can be a continuous function of the bias voltage. Such magnetoasymmetries have been investigated in related mesoscopic systems and arise as a consequence of the asymetric response of the internal potential of the conductor out of equilibrium. Here we discuss magnetoasymmetries in quantum-dot Aharonov-Bohm interferometers when strong electron-electron interactions are taken into account beyond the mean-field approach. We find that at very low temperatures the asymmetric element of the differential conductance shows an abrupt change for voltages around the Fermi level. At higher temperatures we recover a smooth variation of the magnetoasymmetry as a function of the bias. We illustrate our results with the aid of the electron occupation at the dot, demonstrating that its nonequilibrium component is an asymmetric function of the flux even to lowest order in voltage. We also calculate the magnetoasymmetry of the current-current correlations (the noise) and find that it is given, to a good extent, by the magnetoasymmetry of the weakly nonlinear conductance term. Therefore, both magnetoasymmetries (noise and conductance) are related to each other via a higher-order fluctuation-dissipation relation. This result appears to be true even in the low temperature regime, where Kondo physics and many-body effects dominate the transport properties.Comment: 17 pages, 9 figure

A Positive Test for Fermi-Dirac Distributions of Quark-Partons

By describing a large class of deep inelastic processes with standard parameterization for the different parton species, we check the characteristic relationship dictated by Pauli principle: broader shapes for higher first moments. Indeed, the ratios between the second and the first moment and the one between the third and the second moment for the valence partons is an increasing function of the first moment and agrees quantitatively with the values found with Fermi-Dirac distributions.Comment: 15 pages LaTeX, 2 eps figures. Final version, to appear in Mod. Phys. Lett.

The Two-impurity Anderson Model Revisited: Competition between Kondo Effect and Reservoir-mediated Superexchange in Double Quantum Dots

We study a series-coupled double quantum dot in the Kondo regime modeled by the two-impurity Anderson model and find a new conduction-band mediated superexchange interaction that competes with Kondo physics in the strong Coulomb interaction limit. Our numerical renormalization group results, complemented with the higher-order Rayleigh-Schr\"odinger perturbation theory, show that the novel exchange mechanism leads to clear experimental consequences that can be checked in transport measurements through double quantum dots

RKKY and magnetic field interactions in coupled Kondo quantum dots

We investigate theoretically the transport properties of two independent artificial Kondo impurities. They are coupled together via a tunable Ruderman-Kittel-Kasuya-Yoshida (RKKY) interaction. For strong enough antiferromagnetic RKKY interaction, the impurity density of states increases with the applied in-plane magnetic field. This effect can be used to distinguish between antiferromagnetic and ferromagnetic RKKY interactions. These results may be relevant to explain some features of recent experiments by Craig et al. (cond-mat/0404213).Comment: 4 pages, 3 figure

Effect of the Gribov horizon on the Polyakov loop and vice versa

We consider finite temperature SU(2) gauge theory in the continuum formulation, which necessitates the choice of a gauge fixing. Choosing the Landau gauge, the existing gauge copies are taken into account by means of the Gribov-Zwanziger (GZ) quantization scheme, which entails the introduction of a dynamical mass scale (Gribov mass) directly influencing the Green functions of the theory. Here, we determine simultaneously the Polyakov loop (vacuum expectation value) and Gribov mass in terms of temperature, by minimizing the vacuum energy w.r.t. the Polyakov loop parameter and solving the Gribov gap equation. Inspired by the Casimir energy-style of computation, we illustrate the usage of Zeta function regularization in finite temperature calculations. Our main result is that the Gribov mass directly feels the deconfinement transition, visible from a cusp occurring at the same temperature where the Polyakov loop becomes nonzero. In this exploratory work we mainly restrict ourselves to the original Gribov-Zwanziger quantization procedure in order to illustrate the approach and the potential direct link between the vacuum structure of the theory (dynamical mass scales) and (de)confinement. We also present a first look at the critical temperature obtained from the Refined Gribov-Zwanziger approach. Finally, a particular problem for the pressure at low temperatures is reported.Comment: 19 pages, 8 .pdf figures. v2: extended section 3 + extra references; version accepted for publication in EPJ

Transport properties of a molecule embedded in an Aharonov-Bohm interferometer

We theoretically investigate the transport properties of a molecule embedded in one arm of a mesoscopic Aharonov-Bohm interferometer. Due to the presence of phonons the molecule level position ($\epsilon_d$) and the electron-electron interaction ($U$) undergo a \emph{polaronic shift} which affects dramatically the electronic transport through the molecular junction. When the electron-phonon interaction is weak the linear conductance presents Fano-line shapes as long as the direct channel between the electrodes is opened. The observed Fano resonances in the linear conductance are originated from the interference between the spin Kondo state and the direct path. For strong enough electron-phonon interaction, the electron-electron interaction is renormalized towards negative values, {\it i.e.} becomes effectively attractive. This scenario favors fluctuations between the empty and doubly occupied charge states and therefore promotes a charge Kondo effect. However, the direct path between the contacts breaks the electron-hole symmetry which can efficiently suppress this charge Kondo effect. Nevertheless, we show that a proper tuning of the gate voltage is able to revive the Kondo resonance. Our results are obtained by using the Numerical Renormalization approximation to compute the electronic spectral function and the linear conductance.Comment: 17 pages, 12 figure

Brotações epicórmicas no resgate vegetativo de árvores selecionadas de Ilex paraguariensis St. Hil.

Com o objetivo de avaliar a indução de brotações epicórmicas em ramos destacadas de Ilex paraguariensis St. Hil., foram coletados ramos de 60 cm oriundos de um teste combinado de procedências e progênies de 14 anos de idade, em Colombo - PR. Os ramos foram acondicionados em casa de vegetação, nos seguintes tratamentos: T1 = sobre a bancada, T2 = dentro de bandejas com água pura e T3 = dentro de bandeja com areia fina. Foram avaliadas as características sobrevivência e diâmetro do ápice dos ramos, número de tufos e número de brotos produzidos aos 45 e 90 dias. Aos 45 dias, T2 mostrou-se tão eficiente quanto T3 na sobrevivência e número de brotos produzidos, ao passo que aos 90 dias T3 apresentou-se superior em todas as características avaliadas. T1 apresentou baixa produção de tufos e brotos aos 45 dias e mortalidade de 100% dos ramos aos 90 dias. A técnica mostrou-se viável, obtendo-se brotos com tamanho padrão para possível utilização em outras técnicas de propagação vegetativa, sendo a areia superior aos demais tratamentos, ao mesmo tempo em que se mostra menos exigente em manutenção.Secão: Conservação, Melhoramento e Multiplicação. Feira do Agronegócio da Erva-mate, 1., 2003, Chapecó. Integrar para promover o agronegócio da erva-mate

Synthetic spectra of H Balmer and HeI absorption lines. I: Stellar library

We present a grid of synthetic profiles of stellar H Balmer and HeI lines at optical wavelengths with a sampling of 0.3 A. The grid spans a range of effective temperature 4000 K < Teff < 50000 K, and gravity 0.0 < log g < 5.0 at solar metallicity. For Teff > 25000 K, NLTE stellar atmosphere models are computed using the code TLUSTY (Hubeny 1988). For cooler stars, Kurucz (1993) LTE models are used to compute thesynthetic spectra. The grid includes the profiles of the high-order hydrogen Balmer series and HeI lines for effective temperatures and gravities that have not been previously synthesized. The behavior of H8 to H13 and HeI 3819 with effective temperature and gravity is very similar to that of the lower terms of the series (e.g. Hb) and the other HeI lines at longer wavelengths; therefore, they are suited for the determination of the atmospheric parameters of stars. These lines are potentially important to make predictions for these stellar absorption features in galaxies with active star formation. Evolutionary synthesis models of these lines for starburst and post-starburst galaxies are presented in a companion paper. The full set of the synthetic stellar spectra is available for retrieval at our website http://www.iaa.es/ae/e2.html and http://www.stsci.edu/science/starburst/ or on request from the authors at [email protected]: To be published in ApJS. 28 pages and 12 figure

Josephson current in strongly correlated double quantum dots

We study the transport properties of a serial double quantum dot (DQD) coupled to two superconducting leads, focusing on the Josephson current through the DQD and the associated 0-$\pi$ transitions which result from the subtle interplay between the superconductivity, the Kondo physics, and the inter-dot superexchange interaction. We examine the competition between the superconductivity and the Kondo physics by tuning the relative strength $\Delta/T_K$ of the superconducting gap $\Delta$ and the Kondo temperature $T_K$, for different strengths of the superexchange coupling determined by the interdot tunneling $t$ relative to the dot level broadening $\Gamma$. We find strong renormalization of $t$, a significant role of the superexchange coupling $J$, and a rich phase diagram of the 0 and $\pi$-junction regimes. In particular, when both the superconductivity and the exchange interaction are in close competion with the Kondo physics ($\Delta\sim J\sim T_K$), there appears an island of $\pi'$-phase at large values of the superconducting phase difference.Comment: 4 pages, 4 figure

Fósforo, fosfato de rocha e fluorose em bovinos.

Fosfatos naturais na alimentação animal. Uso e abuso dos fosfatos naturais. Essencialidade do flúor. Metabolismo do flúor. Fluor e produção de leite. Flúor e reprodução. O flúor e a barreira placentária. Recuperação do animal exposto ao flúor. Antagonistas do flúor. Efeitos tóxicos do flúor. Diagnóstico de fluorese. Dentição normal dos bovinos. Fluorose dentária.bitstream/item/104565/1/Fosforo-fosfato-de-rocha.pd