22,754 research outputs found

    Possible effects of charge frustration in Nax_xCoO2_2: bandwidth suppression, charge orders and resurrected RVB superconductivity

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    Charge frustration due to further neighbor Coulomb repulsion can have dramatic effects on the electronic properties of Nax_xCoO2_2 in the full doping range. It can significantly reduce the effective mobility of the charge carriers, leading to a low degeneracy temperature ϵFT\epsilon_F \lesssim T. Such strongly renormalized Fermi liquid has rather unusual properties--from the point of view of the ordinary metals with ϵFT\epsilon_F \gg T--but similar to the properties that are actually observed in the Nax_xCoO2_2 system. For example, we show that the anomalous thermopower and Hall effect observed in Na0.7_{0.7}CoO2_2 may be interpreted along these lines. If the repulsion is strong, it can also lead to charge order; nevertheless, away from the commensurate dopings, the configurational constraints allow some mobility for the charge carriers, i.e., there remains some ``metallic'' component. Finally, the particularly strong bandwidth suppression around the commensurate x=1/3x=1/3 can help resurrect the RVB superconductivity, which would otherwise not be expected near this high doping. These suggestions are demonstrated specifically for a tJtJ-like model with an additional nearest neighbor repulsion.Comment: 15 pages, 17 figure

    Expansion dynamics of Lennard-Jones systems

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    The dynamics of the expansion of a Lennard-Jones system, initially confined at high density and subsequently expanding freely in the vacuum, is confronted to an expanding statistical ensemble, derived in the diluted quasi-ideal Boltzmann approximation. The description proves to be fairly accurate at predicting average one-body global observables, but important deviations are observed in the configuration-space structure of the events. Possible implications for finite expanding physical systems are outlined

    Fluid adsorption near an apex: Covariance between complete and critical wetting

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    Critical wetting is an elusive phenomenon for solid-fluid interfaces. Using interfacial models we show that the diverging length scales, which characterize complete wetting at an apex, precisely mimic critical wetting with the apex angle behaving as the contact angle. Transfer matrix, renormalization group (RG) and mean field analysis (MF) shows this covariance is obeyed in 2D, 3D and for long and short ranged forces. This connection should be experimentally accesible and provides a means of checking theoretical predictions for critical wetting.Comment: 4 pages, 1 figure, submitted to Physical Review Letter

    Mapping the phase diagram of strongly interacting matter

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    We employ a conformal mapping to explore the thermodynamics of strongly interacting matter at finite values of the baryon chemical potential μ\mu. This method allows us to identify the singularity corresponding to the critical point of a second-order phase transition at finite μ\mu, given information only at μ=0\mu=0. The scheme is potentially useful for computing thermodynamic properties of strongly interacting hot and dense matter in lattice gauge theory. The technique is illustrated by an application to a chiral effective model.Comment: 5 pages, 3 figures; published versio

    Coupled Fluctuations near Critical Wetting

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    Recent work on the complete wetting transition has emphasized the role played by the coupling of fluctuations of the order parameter at the wall and at the depinning fluid interface. Extending this approach to the wetting transition itself we predict a novel crossover effect associated with the decoupling of fluctuations as the temperature is lowered towards the transition temperature T_W. Using this we are able to reanalyse recent Monte-Carlo simulation studies and extract a value \omega(T_W)=0.8 at T_W=0.9T_C in very good agreement with long standing theoretical predictions.Comment: 4 pages, LaTex, 1 postscript figur

    Depinning with dynamic stress overshoots: A hybrid of critical and pseudohysteretic behavior

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    A model of an elastic manifold driven through a random medium by an applied force F is studied focussing on the effects of inertia and elastic waves, in particular {\it stress overshoots} in which motion of one segment of the manifold causes a temporary stress on its neighboring segments in addition to the static stress. Such stress overshoots decrease the critical force for depinning and make the depinning transition hysteretic. We find that the steady state velocity of the moving phase is nevertheless history independent and the critical behavior as the force is decreased is in the same universality class as in the absence of stress overshoots: the dissipative limit which has been studied analytically. To reach this conclusion, finite-size scaling analyses of a variety of quantities have been supplemented by heuristic arguments. If the force is increased slowly from zero, the spectrum of avalanche sizes that occurs appears to be quite different from the dissipative limit. After stopping from the moving phase, the restarting involves both fractal and bubble-like nucleation. Hysteresis loops can be understood in terms of a depletion layer caused by the stress overshoots, but surprisingly, in the limit of very large samples the hysteresis loops vanish. We argue that, although there can be striking differences over a wide range of length scales, the universality class governing this pseudohysteresis is again that of the dissipative limit. Consequences of this picture for the statistics and dynamics of earthquakes on geological faults are briefly discussed.Comment: 43 pages, 57 figures (yes, that's a five followed by a seven), revte

    Gas-liquid critical point in ionic fluids

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    Based on the method of collective variables we develop the statistical field theory for the study of a simple charge-asymmetric 1:z1:z primitive model (SPM). It is shown that the well-known approximations for the free energy, in particular DHLL and ORPA, can be obtained within the framework of this theory. In order to study the gas-liquid critical point of SPM we propose the method for the calculation of chemical potential conjugate to the total number density which allows us to take into account the higher order fluctuation effects. As a result, the gas-liquid phase diagrams are calculated for z=24z=2-4. The results demonstrate the qualitative agreement with MC simulation data: critical temperature decreases when zz increases and critical density increases rapidly with zz.Comment: 18 pages, 1 figur

    Ionic fluids: charge and density correlations near gas-liquid criticality

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    The correlation functions of an ionic fluid with charge and size asymmetry are studied within the framework of the random phase approximation. The results obtained for the charge-charge correlation function demonstrate that the second-moment Stillinger-Lovett (SL) rule is satisfied away from the gas-liquid critical point (CP) but not, in general, at the CP. However in the special case of a model without size assymetry the SL rules are satisfied even at the CP. The expressions for the density-density and charge-density correlation functions valid far and close to the CP are obtained explicitely

    Local functional models of critical correlations in thin-films

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    Recent work on local functional theories of critical inhomogeneous fluids and Ising-like magnets has shown them to be a potentially exact, or near exact, description of universal finite-size effects associated with the excess free-energy and scaling of one-point functions in critical thin films. This approach is extended to predict the two-point correlation function G in critical thin-films with symmetric surface fields in arbitrary dimension d. In d=2 we show there is exact agreement with the predictions of conformal invariance for the complete spectrum of correlation lengths as well as the detailed position dependence of the asymptotic decay of G. In d=3 and d>=4 we present new numerical predictions for the universal finite-size correlation length and scaling functions determining the structure of G across the thin-film. Highly accurate analytical closed form expressions for these universal properties are derived in arbitrary dimension.Comment: 4 pages, 1 postscript figure. Submitted to Phys Rev Let

    Weakly versus highly nonlinear dynamics in 1D systems

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    We analyze the morphological transition of a one-dimensional system described by a scalar field, where a flat state looses its stability. This scalar field may for example account for the position of a crystal growth front, an order parameter, or a concentration profile. We show that two types of dynamics occur around the transition: weakly nonlinear dynamics, or highly nonlinear dynamics. The conditions under which highly nonlinear evolution equations appear are determined, and their generic form is derived. Finally, examples are discussed.Comment: to be published in Europhys. Let
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