9,924 research outputs found

    Competing Glauber and Kawasaki Dynamics

    Full text link
    Using a quantum formulation of the master equation we study a kinetic Ising model with competing stochastic processes: the Glauber dynamics with probability pp and the Kawasaki dynamics with probability 1p1 - p. Introducing explicitely the coupling to a heat bath and the mutual static interaction of the spins the model can be traced back exactly to a Ginzburg Landau functional when the interaction is of long range order. The dependence of the correlation length on the temperature and on the probability pp is calculated. In case that the spins are subject to flip processes the correlation length disappears for each finite temperature. In the exchange dominated case the system is strongly correlated for each temperature.Comment: 9 pages, Revte

    Non-equilibrium dynamics of the Bose-Hubbard model: A projection operator approach

    Full text link
    We study the phase diagram and non-equilibrium dynamics, both subsequent to a sudden quench of the hopping amplitude JJ and during a ramp J(t)=Jt/τJ(t)=Jt/\tau with ramp time τ\tau, of the Bose-Hubbard model at zero temperature using a projection operator formalism which allows us to incorporate the effects of quantum fluctuations beyond mean-field approximations in the strong coupling regime. Our formalism yields a phase diagram which provides a near exact match with quantum Monte Carlo results in three dimensions. We also compute the residual energy QQ, the superfluid order parameter Δ(t)\Delta(t), the equal-time order parameter correlation function C(t)C(t), and the wavefunction overlap FF which yields the defect formation probability PP during non-equilibrium dynamics of the model. We find that QQ, FF, and PP do not exhibit the expected universal scaling. We explain this absence of universality and show that our results compare well with recent experiments.Comment: Replaced with the accepted version, added one figure. 4 pages, 4 figures, to appear in Phys. Rev. Let

    Broad Line Radio Galaxies: Jet Contribution to the nuclear X-Ray Continuum

    Get PDF
    It is shown that, for Broad Line Radio Galaxies the strength of the non-thermal beamed radiation, when present, is always smaller than the accretion flow by a factor < 0.7 in the 2-10 keV band. The result has been obtained using the procedure adopted for disentangling the Flat Spectrum Radio Quasar 3C 273 (Grandi & Palumbo 2004). Although this implies a significantly smaller non-thermal flux in Radio Galaxies when compared to Blazars, the jet component, if present, could be important at very high energies and thus easily detectable with GLAST.Comment: 12 pages including 2 figures (4 files), ApJ accepte

    A projection operator approach to the Bose-Hubbard model

    Full text link
    We develop a projection operator formalism for studying both the zero temperature equilibrium phase diagram and the non-equilibrium dynamics of the Bose-Hubbard model. Our work, which constitutes an extension of Phys. Rev. Lett. {\bf 106}, 095702 (2011), shows that the method provides an accurate description of the equilibrium zero temperature phase diagram of the Bose-Hubbard model for several lattices in two- and three-dimensions (2D and 3D). We show that the accuracy of this method increases with the coordination number z0z_0 of the lattice and reaches to within 0.5% of quantum Monte Carlo data for lattices with z0=6z_0=6. We compute the excitation spectra of the bosons using this method in the Mott and the superfluid phases and compare our results with mean-field theory. We also show that the same method may be used to analyze the non-equilibrium dynamics of the model both in the Mott phase and near the superfluid-insulator quantum critical point where the hopping amplitude JJ and the on-site interaction UU satisfy z0J/U1z_0J/U \ll 1. In particular, we study the non-equilibrium dynamics of the model both subsequent to a sudden quench of the hopping amplitude JJ and during a ramp from JiJ_i to JfJ_f characterized by a ramp time τ\tau and exponent α\alpha: J(t)=Ji+(JfJi)(t/τ)αJ(t)=J_i +(J_f-J_i) (t/\tau)^{\alpha}. We compute the wavefunction overlap FF, the residual energy QQ, the superfluid order parameter Δ(t)\Delta(t), the equal-time order parameter correlation function C(t)C(t), and the defect formation probability PP for the above-mentioned protocols and provide a comparison of our results to their mean-field counterparts. We find that QQ, FF, and PP do not exhibit the expected universal scaling. We explain this absence of universality and show that our results for linear ramps compare well with the recent experimental observations.Comment: v2; new references and new sections adde

    Phenomenological Renormalization Group Methods

    Full text link
    Some renormalization group approaches have been proposed during the last few years which are close in spirit to the Nightingale phenomenological procedure. In essence, by exploiting the finite size scaling hypothesis, the approximate critical behavior of the model on infinite lattice is obtained through the exact computation of some thermal quantities of the model on finite clusters. In this work some of these methods are reviewed, namely the mean field renormalization group, the effective field renormalization group and the finite size scaling renormalization group procedures. Although special emphasis is given to the mean field renormalization group (since it has been, up to now, much more applied an extended to study a wide variety of different systems) a discussion of their potentialities and interrelations to other methods is also addressed.Comment: Review Articl

    Topological properties of the bond-modulated honeycomb lattice

    Get PDF
    We study the combined effects of lattice deformation, e-e interaction and spin-orbit coupling in a two-dimensional (2D) honeycomb lattice. We adopt different kinds of hopping modulation--generalized dimerization and a Kekule distortion--and calculate topological invariants for the non-interacting system and for the interacting system. We identify the parameter range (Hubbard U, hopping modulation, spin-orbit coupling) where the 2D system behaves as a trivial insulator or Quantum Spin Hall Insulator.Comment: 8 pages, 4 figures: discussion improved, typos corrected, references updated. Matches version published in PR
    corecore