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(314) Production(s) de BERTHIER L.


Glassy dynamics of athermal selfpropelled particles: Computer simulations and a nonequilibrium microscopic theory
Auteur(s): Szamel G., Flenner Elijah, Berthier L.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 91 p.062304 (2015)
Texte intégral en Openaccess :
Ref HAL: hal01163076_v1
Ref Arxiv: 1501.01333
DOI: 10.1103/PhysRevE.91.062304
WoS: 000355973500005
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
62 Citations
Résumé: We combine computer simulations and analytical theory to investigate the glassy dynamics in dense assemblies of athermal particles evolving under the sole influence of selfpropulsion. The simulations reveal that when the persistence time of the selfpropelled particles is increased, the local structure becomes more pronounced whereas the longtime dynamics first accelerates and then slows down. These seemingly contradictory evolutions are explained by constructing a nonequilibrium modecouplinglike theory for interacting selfpropelled particles. To predict the collective dynamics the theory needs the steady state structure factor and the steady state correlations of the local velocities. It yields nontrivial predictions for the glassy dynamics of selfpropelled particles in qualitative agreement with the simulations.
Commentaires: 9 pages; accepted for publication in Physical Review E



Evidence for a disordered critical point in a glassforming liquid
Auteur(s): Berthier L., Jack Robert L.
(Article) Publié:
Physical Review Letters, vol. 114 p.205701 (2015)
Texte intégral en Openaccess :
Ref HAL: hal01157941_v1
PMID 26047241
Ref Arxiv: 1503.08576
DOI: 10.1103/PhysRevLett.114.205701
WoS: 000354928700005
Ref. & Cit.: NASA ADS
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40 Citations
Résumé: Using computer simulations of an atomistic glassforming liquid, we investigate the fluctuations of the overlap between a fluid configuration and a quenched reference system. We find that large fluctuations of the overlap develop as temperature decreases, consistent with the existence of the random critical point that is predicted by effective field theories. We discuss the scaling of fluctuations near the presumed critical point, comparing the observed behaviour with that of the randomfield Ising model. We argue that this critical point directly reveals the existence of an interfacial tension between amorphous metastable states, a quantity relevant both for equilibrium relaxation and for nonequilibrium melting of stable glass configurations.
Commentaires: 4 figs, 5 pages. Réf Journal: Phys. Rev. Lett. 114, 205701 (2015)



Relaxation dynamics in a transient network fluid with competing gel and glass phases
Auteur(s): Chaudhuri Pinaki, Hurtado Pablo i., Berthier L., Kob W.
(Article) Publié:
The Journal Of Chemical Physics, vol. 142 p.174503 (2015)
Texte intégral en Openaccess :
Ref HAL: hal01152155_v1
PMID 25956109
DOI: 10.1063/1.4919645
WoS: 000354258200032
Exporter : BibTex  endNote
14 Citations
Résumé: We use computer simulations to study the relaxation dynamics of a model for oilinwater microemulsion droplets linked with telechelic polymers. This system exhibits both gel and glass phases and we show that the competition between these two arrest mechanisms can result in a complex, threestep decay of the time correlation functions, controlled by two different localization lengthscales. For certain combinations of the parameters, this competition gives rise to an anomalous logarithmic decay of the correlation functions and a subdiffusive particle motion, which can be understood as a simple crossover effect between the two relaxation processes. We establish a simple criterion for this logarithmic decay to be observed. We also find a further logarithmically slow relaxation related to the relaxation of floppy clusters of particles in a crowded environment, in agreement with recent findings in other models for dense chemical gels. Finally, we characterize how the competition of gel and glass arrest mechanisms affects the dynamical heterogeneities and show that for certain combination of parameters these heterogeneities can be unusually large. By measuring the fourpoint dynamical susceptibility, we probe the cooperativity of the motion and find that with increasing coupling this cooperativity shows a maximum before it decreases again, indicating the change in the nature of the relaxation dynamics. Our results suggest that compressing gels to large densities produces novel arrested phases that have a new and complex dynamics.



Hyperuniform density fluctuations and diverging dynamic correlations in periodically driven colloidal suspensions
Auteur(s): Tjhung E., Berthier L.
(Article) Publié:
Physical Review Letters, vol. 114 p.148301 (2015)
Texte intégral en Openaccess :
Ref HAL: hal01140762_v1
PMID 25910165
Ref Arxiv: 1501.05633
DOI: 10.1103/PhysRevLett.114.148301
WoS: 000352350000014
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75 Citations
Résumé: The emergence of particle irreversibility in periodically driven colloidal suspensions has been interpreted as resulting either from a nonequilibrium phase transition to an absorbing state or from the chaotic nature of particle trajectories. Using a simple model of a driven suspension we show that a nonequilibrium phase transition is accompanied by hyperuniform static density fluctuations in the vicinity of the transition, where we also observe strong dynamic heterogeneities reminiscent of dynamics in glassy materials. We find that single particle dynamics becomes intermittent and strongly nonFickian, and that collective dynamics becomes spatially correlated over diverging lengthscales. Our results suggest that the two theoretical scenarii can be experimentally discriminated using particleresolved measurements of standard static and dynamic observables.
Commentaires: 5 pages; v2 accepted for publication in Phys. Rev. Lett



Nonequilibrium equation of state in suspensions of active colloids
Auteur(s): Ginot Félix, Theurkauff Isaac, Levis D., Ybert Christophe, Bocquet Lydéric, Berthier L., CottinBizonne Cécile
(Article) Publié:
Physical Review, vol. 5 p.011004 (2015)
Texte intégral en Openaccess :
Ref HAL: hal01132427_v1
Ref Arxiv: 1411.7175
DOI: 10.1103/PhysRevX.5.011004
WoS: 000349488400001
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187 Citations
Résumé: Active colloids constitute a novel class of materials composed of colloidalscale particles locally converting chemical energy into motility, mimicking microorganisms. Evolving far from equilibrium, these systems display structural organizations and dynamical properties distinct from thermalized colloidal assemblies. Harvesting the potential of this new class of systems requires the development of a conceptual framework to describe these intrinsically nonequilibrium systems. We use sedimentation experiments to probe the nonequilibrium equation of state of a bidimensional assembly of active Janus microspheres, and conduct computer simulations of a model of selfpropelled hard disks. Selfpropulsion profoundly affects the equation of state, but these changes can be rationalized using equilibrium concepts. We show that active colloids behave, in the dilute limit, as an ideal gas with an activitydependent effective temperature. At finite density, increasing the activity is similar to increasing adhesion between equilibrium particles. We quantify this effective adhesion and obtain a unique scaling law relating activity and effective adhesion in both experiments and simulations. Our results provide a new and efficient way to understand the emergence of novel phases of matter in active colloidal suspensions.
Commentaires: 8 pages, 4 figs; to be published in Phys. Rev. X. Réf Journal: Phys. Rev. X 5, 011004 (2015)



Diverging viscosity and soft granular rheology in nonBrownian suspensions
Auteur(s): Kawasaki T., Coslovich D., Ikeda A., Berthier L.
(Article) Publié:
Physical Review E: Statistical, Nonlinear, And Soft Matter Physics, vol. 91 p.012203 (2015)
Texte intégral en Openaccess :
Ref HAL: hal01115925_v1
PMID 25679615
Ref Arxiv: 1410.5683
DOI: 10.1103/PhysRevE.91.012203
WoS: 000348681000006
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47 Citations
Résumé: We use large scale computer simulations and finite size scaling analysis to study the shear rheology of dense threedimensional suspensions of frictionless nonBrownian particles in the vicinity of the jamming transition. We perform simulations of soft repulsive particles at constant shear rate, constant pressure, and finite system size, and study carefully the asymptotic limits of large system sizes and infinitely hard particle repulsion. Extending earlier analysis by about two orders of magnitude, we first study the asymptotic behavior of the shear viscosity in the hard particle limit. We confirm its asymptotic power law divergence at the jamming transition, but show that a precise determination of the critical density and critical exponent is difficult due to the `multiscaling' behavior of the viscosity. Additionally, finitesize scaling analysis suggests that this divergence is accompanied by a growing correlation length scale, which also diverges algebraically. We then study the effect of soft repulsion, and propose a natural extension of the standard granular rheology to account for softness effects, which we validate from simulations. Close to the jamming transition, this `soft granular rheology' offers a detailed description of the nonlinear rheology of soft particles, which differs from earlier empirical scaling forms.
Commentaires: 12 pages, 9 figs. Réf Journal: Phys. Rev. E 91, 012203 (2015)



Equilibrium ultrastable glasses produced by random pinning
Auteur(s): Hocky Glen M, Berthier L., Reichman David R.
(Article) Publié:
The Journal Of Chemical Physics, vol. 141 p.224503 (2014)
Texte intégral en Openaccess :
Ref HAL: hal01104689_v1
PMID 25494756
Ref Arxiv: 1409.6730
DOI: 10.1063/1.4903200
WoS: 000346272800032
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Exporter : BibTex  endNote
24 Citations
Résumé: Ultrastable glasses have risen to prominence due to their potentially useful material properties and the tantalizing possibility of a general method of preparation via vapor deposition. Despite the importance of this novel class of amorphous materials, numerical studies have been scarce because achieving ultrastability in atomistic simulations is an enormous challenge. Here we bypass this difficulty and establish that randomly pinning the position of a small fraction of particles inside an equilibrated supercooled liquid generates ultrastable configurations at essentially no numerical cost, while avoiding undesired structural changes due to the preparation protocol. Building on the analogy with vapordeposited ultrastable glasses, we study the melting kinetics of these configurations following a sudden temperature jump into the liquid phase. In homogeneous geometries, we find that enhanced kinetic stability is accompanied by large scale dynamic heterogeneity, while a competition between homogeneous and heterogeneous melting is observed when a liquid boundary invades the glass at constant velocity. Our work demonstrates the feasibility of largescale, atomistically resolved, and experimentally relevant simulations of the kinetics of ultrastable glasses.
Commentaires: 9 pages, 5 figures. Réf Journal: Journal of Chemical Physics 141, 224503 (2014)
