545 research outputs found

    Monte-Carlo simulations of the violation of the fluctuation-dissipation theorem in domain growth processes

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    Numerical simulations of various domain growth systems are reported, in order to compute the parameter describing the violation of fluctuation dissipation theorem (FDT) in aging phenomena. We compute two-times correlation and response functions and find that, as expected from the exact solution of a certain mean-field model (equivalent to the O(N) model in three dimensions, in the limit of N going to infinity), this parameter is equal to one (no violation of FDT) in the quasi-equilibrium regime (short separation of times), and zero in the aging regime.Comment: 5 pages, 5 eps figure

    Effective temperature of a dissipative driven mesoscopic system

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    We study the nonequilibrium dynamics of a mesoscopic metallic ring threaded by a time-dependent magnetic field and coupled to an electronic reservoir. We analyze the relation between the (non-stationary) real-time Keldysh and retarded Green functions and we find that, in the linear response regime with weak heat transfer to the environment, an effective temperature accounts for the modification of the equilibrium fluctuation-dissipation relation. We discuss possible extensions of this analysis.Comment: 4 pages, 4 figures, RevTe

    Dissipative quantum disordered models

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    This article reviews recent studies of mean-field and one dimensional quantum disordered spin systems coupled to different types of dissipative environments. The main issues discussed are: (i) The real-time dynamics in the glassy phase and how they compare to the behaviour of the same models in their classical limit. (ii) The phase transition separating the ordered -- glassy -- phase from the disordered phase that, for some long-range interactions, is of second order at high temperatures and of first order close to the quantum critical point (similarly to what has been observed in random dipolar magnets). (iii) The static properties of the Griffiths phase in random Ising chains. (iv) The dependence of all these properties on the environment. The analytic and numeric techniques used to derive these results are briefly mentioned.Comment: Contribution to the 12th International Conference on Recent Progress in Many-Body Theories, Santa Fe, New Mexico, USA, August 2004; 10 pages no fig

    Comment on "Fluctuation-dissipation relations in the nonequilibrium critical dynamics of Ising models"

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    Recently Mayer et al. [Phys. Rev. E {\bf 68}, 016116 (2003)] proposed a new way to compute numerically the fluctuation-dissipation ratios in nonequilibrium critical systems. Using well-known facts of nonequilibrium critical dynamics I show that the leading contributions of the quantities they consider are in fact one-time quantities which are independent of the waiting time. The ratio of these one-time quantities determines the slope of the straight lines observed in the fluctuation-dissipation plots of Mayer et al.Comment: 4 pages, 3 figures included, shortened versio

    Memory effects in classical and quantum mean-field disordered models

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    We apply the Kovacs experimental protocol to classical and quantum p-spin models. We show that these models have memory effects as those observed experimentally in super-cooled polymer melts. We discuss our results in connection to other classical models that capture memory effects. We propose that a similar protocol applied to quantum glassy systems might be useful to understand their dynamics.Comment: 24 pages, 12 figure

    Dynamical fluctuations in an exactly solvable model of spin glasses

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    In this work we calculate the dynamical fluctuations at O(1/N) in the low temperature phase of the p=2p=2 spherical spin glass model. We study the large-times asymptotic regimes and we find, in a short time-differences regime, a fluctuation dissipation relation for the four-point correlation functions. This relation can be extended to the out of equilibrium regimes introducing a function XtX_{t} which, for large time tt, we find scales as t−1/2t^{-1/2} as in the case of the two-point functions.Comment: Latex, 8 page

    Evidence of aging in mean-field spin glass models

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    We study numerically the out of equilibrium dynamics of the hypercubic cell spin glass in high dimensionalities. We obtain evidence of aging effects qualitatively similar both to experiments and to simulations of low dimensional models. This suggests that the Sherrington-Kirkpatrick model as well as other mean-field finite connectivity lattices can be used to study these effects analytically.Comment: 13 pages + 5 figures (upon request

    Relaxation dynamics of the Ising pp-spin disordered model with finite number of variables

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    We study the dynamic and metastable properties of the fully connected Ising pp-spin model with finite number of variables. We define trapping energies, trapping times and self correlation functions and we analyse their statistical properties in comparison to the predictions of trap models.Comment: 7 pages, 6 figures, final versio

    Off-Equilibrium Effective Temperature in Monatomic Lennard-Jones Glass

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    The off-equilibrium dynamics of a monatomic Lennard-Jones glass is investigated after sudden isothermal density jumps (crunch) from well equilibrated liquid configurations towards the glassy state. The generalized fluctuation-dissipation relation has been studied and the temperature dependence of the violation factor m is found in agreement with the one step replica symmetry breaking scenario, i.e. at low temperature m(T) is found proportional to T up to an off-equilibrium effective temperature T_eff, where m(T_eff)=1. We report T_eff as a function of the density and compare it with the glass transition temperatures T_g as determined by equilibrium calculations.Comment: 4 pages,4 figure
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