Ref HAL: hal-01360538_v1
Ref Arxiv: 1511.04201
DOI: 10.1073/pnas.1607730113
WoS: 000380346200037
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
55 Citations
Résumé:

Low-temperature properties of crystalline solids can be understood using harmonic perturbations around a perfect lattice, as in Debye's theory. Low-temperature properties of amorphous solids, however, strongly depart from such descriptions, displaying enhanced transport, activated slow dynamics across energy barriers, excess vibrational modes with respect to Debye's theory (i.e., a Boson Peak), and complex irreversible responses to small mechanical deformations. These experimental observations indirectly suggest that the dynamics of amorphous solids becomes anomalous at low temperatures. Here, we present direct numerical evidence that vibrations change nature at a well-defined location deep inside the glass phase of a simple glass former. We provide a real-space description of this transition and of the rapidly growing time and length scales that accompany it. Our results provide the seed for a universal understanding of low-temperature glass anomalies within the theoretical framework of the recently discovered Gardner phase transition.

Commentaires: 12 pages, 20 figures. Accepted for publication in PNAS. Réf Journal: PNAS 113, 8397-8401 (2016)

Ref HAL: hal-01353499_v1
Ref Arxiv: 1603.05017
DOI: 10.1063/1.4954327
WoS: 000379166100038
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
10 Citations
Résumé:

We discuss the microscopic mechanisms by which low-temperature amorphous states, such as ultrastable glasses, transform into equilibrium fluids, after a sudden temperature increase. Experiments suggest that this process is similar to the melting of crystals, thus differing from the behaviour found in ordinary glasses. We rationalize these observations using the physical idea that the transformation process takes place very close to a `hidden' equilibrium first-order phase transition, which is observed in systems of coupled replicas. We illustrate our views using simulation results for a simple two-dimensional plaquette spin model, which is known to exhibit a range of glassy behaviour. Our results suggest that nucleation-and-growth dynamics, as found near ordinary first-order transitions, is also the correct theoretical framework to analyse the melting of ultrastable glasses. Our approach provides a unified understanding of multiple experimental observations, such as propagating melting fronts, large kinetic stability ratios, and `giant' dynamic lengthscales.

Commentaires: 15 pages, 9 figs. Réf Journal: J. Chem. Phys. 144, 244506 (2016)

Ref HAL: hal-01331594_v1
Ref Arxiv: 1511.06182
DOI: 10.1103/PhysRevLett.116.238002
WoS: 000377509900014
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
76 Citations
Résumé:

We implement and optimize a particle-swap Monte-Carlo algorithm that allows us to thermalize a polydisperse system of hard spheres up to unprecedentedly-large volume fractions, where \revise{previous} algorithms and experiments fail to equilibrate. We show that no glass singularity intervenes before the jamming density, which we independently determine through two distinct non-equilibrium protocols. We demonstrate that equilibrium fluid and non-equilibrium jammed states can have the same density, showing that the jamming transition cannot be the end-point of the fluid branch.

Commentaires: 5 pages, 3 figs; To be published in Phys. Rev. Lett. Réf Journal: Phys. Rev. Lett. 116, 238002 (2016)

Ref HAL: hal-01310551_v1
Ref Arxiv: 1602.04796
DOI: 10.1103/PhysRevLett.116.179801
WoS: 000374963700003
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
2 Citations
Résumé:

In a recent Letter, Wang and Brady (WB) [1] analyse the rheology of Brownian hard spheres using constant stress and pressure Brownian dynamics simulations. The main observable is the shear viscosity, η( ̇γ,Π), expressed as a function of the shear rate ̇γ and adimensional pressure ̄Π = Πa3/(kBT), where Π is the pressure, kBT the thermal energy, and a the average particle diameter. The central conclusion is the discovery of a “universal viscosity divergence”

Commentaires: 1 page; under review

Ref HAL: hal-01294277_v1
Ref Arxiv: 1510.07916
DOI: 10.1088/1742-5468/2016/03/033501
WoS: 000375704700040
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
11 Citations
Résumé:

One possible framework to interpret the irreversibility transition observed in periodically driven colloidal suspensions is that of a non-equilibrium phase transition towards an absorbing reversible state at low amplitude of the driving force. We consider a simple numerical model for driven suspensions which allows us to characterize in great detail a large body of physical observables that can be experimentally determined to assess the existence and universality class of such a non-equilibrium phase transition. Characterizing the behaviour of static and dynamic correlation functions both in real and Fourier space we determine in particular several critical exponents for our model, which take values that are in good agreement with the universality class of direct ed percolation. We also provide a detailed analysis of single-particle and collective dynamics of the system near the phase transition, which appear intermittent and spatially correlated over diverging timescales and lengthscales, and provide clear signatures of the underlying criticality.

Commentaires: 27 pages, 12 figures; J. Stat. Mech. (in press)

Ref HAL: hal-01261246_v2
Ref Arxiv: 1510.06320
DOI: 10.1063/1.4939640
WoS: 000368618400033
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
17 Citations
Résumé:

Cavity point-to-set correlations are real-space tools to detect the roughening of the free-energy landscape that accompanies the dynamical slowdown of glass-forming liquids. Measuring these correlations in model glass formers remains, however, a major computational challenge. Here, we develop a general parallel-tempering method that provides orders-of-magnitude improvement for sampling and equilibrating configurations within cavities. We apply this improved scheme to the canonical Kob-Andersen binary Lennard-Jones model for temperatures down to the mode-coupling theory crossover. Most significant improvements are noted for small cavities, which have thus far been the most difficult to study. This methodological advance also enables us to study a broader range of physical observables associated with thermodynamic fluctuations. We measure the probability distribution of overlap fluctuations in cavities, which displays a non-trivial temperature evolution. The corresponding overlap susceptibility is found to provide a robust quantitative estimate of the point-to-set length scale requiring no fitting. By resolving spatial fluctuations of the overlap in the cavity, we also obtain quantitative information about the geometry of overlap fluctuations. We can thus examine in detail how the penetration length as well as its fluctuations evolve with temperature and cavity size.

Commentaires: 12 pages, 7 figures; v2: minor revisions made, figure 1b added, Sec.V extensively revised for clarification, references added. Réf Journal: J. Chem. Phys. 144, 024501 (2016)

Ref HAL: hal-01252109_v1
Ref Arxiv: 1512.03540
DOI: 10.1063/PT.3.3052
WoS: 000393115600013
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
93 Citations
Résumé:

Glasses constitute a widespread form of solid matter, and glass production has been an important human technology for more than 3000 years. Despite that long history, new ways to understand the fundamental physics of glasses continue to emerge.

Commentaires: 13 pages, 5 figures. To appear in the January 2016 issue of Physics Today (in press). Réf Journal: Physics Today 69, 40 (2016)