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Ref Arxiv: 1905.08179
DOI: 10.1063/1.5113477
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9 Citations
Résumé:

We perform stringent tests of thermodynamic theories of the glass transition over the experimentally relevant temperature regime for several simulated glass-formers. The swap Monte Carlo algorithm is used to estimate the configurational entropy and static point-to-set lengthscale, and careful extrapolations are used for the relaxation times. We first quantify the relation between configurational entropy and the point-to-set lengthscale in two and three dimensions. We then show that the Adam-Gibbs relation is generally violated in simulated models for the experimentally relevant time window. Collecting experimental data for several supercooled molecular liquids, we show that the same trends are observed experimentally. Deviations from the Adam-Gibbs relation remain compatible with random first order transition theory, and may account for the reported discrepancies between Kauzmann and Vogel-Fulcher-Tammann temperatures. Alternatively, they may also indicate that even near $T_g$ thermodynamics is not the only driving force for slow dynamics.

Commentaires: 13 pages, 8 figures. Réf Journal: J. Chem. Phys. 151, 084504 (2019)

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PMID 31433423
Ref Arxiv: 1812.08736
DOI: 10.1039/c9sm01092k
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36 Citations
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Understanding the difference between universal low-temperature properties of amorphous and crystalline solids requires an explanation of the stronger damping of long-wavelength phonons in amorphous solids. A longstanding sound attenuation scenario, resulting from a combination of experiments, theories, and simulations, leads to a quartic scaling of sound attenuation with the wavevector, which is commonly attributed to Rayleigh scattering of the sound. Modern computer simulations offer conflicting conclusions regarding the validity of this picture. We simulate glasses with an unprecedentedly broad range of stabilities to perform the first microscopic analysis of sound damping in model glass formers across a range of experimentally relevant preparation protocols. We present a convincing evidence that quartic scaling is recovered for small wavevectors irrespective of the glass's stability. With increasing stability, the wavevector where the quartic scaling begins increases by approximately a factor of three and the sound attenuation decreases by over an order of magnitude. Our results uncover an intimate connection between glass stability and sound damping.

Commentaires: 8 pages, 8 figures. Réf Journal: Soft Matter 15, 7018 (2019)

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Ref Arxiv: 1902.10494
DOI: 10.1063/1.5097175
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10 Citations
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One of the most remarkable predictions to emerge out of the exact infinite-dimensional solution of the glass problem is the Gardner transition.Although this transition was first theoretically proposed a generation ago for certain mean-field spin glass models, its materials relevance wasonly realized when a systematic effort to relate glass formation and jamming was undertaken. A number of nontrivial physical signaturesassociated with the Gardner transition have since been considered in various areas, from models of structural glasses to constraint satisfactionproblems. This perspective surveys these recent advances and discusses the novel research opportunities that arise from them.

Commentaires: 17 pages, 9 figures. Réf Journal: J. Chem. Phys. 151, 010901 (2019)

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Ref Arxiv: 1903.02778
DOI: 10.1103/PhysRevB.99.224425
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2 Citations
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We present the full phase diagram of the dumbbell model of spin ice as a function of temperature, chemical potential and staggered chemical potential which breaks the translational lattice symmetry in favour of charge crystal ordering. We observe a double winged structure with five possible phases, monopole fluid (spin ice), fragmented single monopole crystal phases and double monopole crystal, the zinc blend structure. Our model provides a skeleton for liquid-liquid phase transitions and for the winged structures observed for itinerant magnets under pressure and external field. We relate our results to recent experiments on Ho$_2$Ir$_2$O$_7$ and propose a wide ranging set of new experiments that exploit the phase diagram, including high pressure protocols, dynamical scaling of Kibble-Zurek form and universal violations of the fluctuation-dissipation theorem.

Commentaires: 14 pages, 14 figures. Réf Journal: Phys. Rev. B 99, 224425 (2019)

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DOI: 10.1088/1742-5468/ab1910
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39 Citations
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It was recently demonstrated that a simple Monte Carlo (MC) algorithm involving the swap of particle pairs dramatically accelerates the equilibrium sampling of simulated supercooled liquids. We propose two numerical schemes integrating the efficiency of particle swaps into equilibrium molecular dynamics (MD) simulations. We first develop a hybrid MD/MC scheme combining molecular dynamics with the original swap Monte Carlo. We implement this hybrid method in LAMMPS, a software package employed by a large community of users. Secondly, we define a continuous time version of the swap algorithm where both the positions and diameters of the particles evolve via Hamilton's equations of motion. For both algorithms, we discuss in detail various technical issues as well as the optimisation of simulation parameters. We compare the numerical efficiency of all available swap algorithms and discuss their relative merits.

Ref HAL: hal-02180202_v1
DOI: 10.1103/PhysRevLett.122.255502
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We show numerically that a three-dimensional model for structural glass displays aging, rejuvenation, and memory effects when subjected to a temperature cycle. These effects indicate that the free energy landscape of structural glasses may possess the complex hierarchical structure that characterizes materials such as spin and polymer glasses. We use the theoretical concept of marginal stability to interpret our results, and explain in which physical conditions a complex aging dynamics can emerge in dense supercooled liquids, paving the way for future experimental studies of complex aging dynamics in colloidal and granular glasses.

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Ref Arxiv: 1902.08580
DOI: 10.1063/1.5093240
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15 Citations
Résumé:

Despite the diversity of materials designated as active matter, virtually all active systems undergo a form of dynamic arrest when crowding and activity compete, reminiscent of the dynamic arrest observed in colloidal and molecular fluids undergoing a glass transition. We present a short perspective on recent and ongoing efforts to understand how activity competes with other physical interactions in dense systems. We first review recent experimental work on active materials that uncovered both classic signatures of glassy dynamics and intriguing novel phenomena at large density. We introduce a minimal model of self-propelled particles where the competition between interparticle interactions, crowding, and self-propulsion can be studied in great detail. We discuss more complex models that include some additional, material-specific ingredients. We end with some general perspectives on dense active materials, suggesting directions for future research, in particular for theoretical work.

Commentaires: 16 pages, 8 figures. Réf Journal: J. Chem. Phys. 150, 200901 (2019)