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(327) Production(s) de BERTHIER L.
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Collective dynamics in a glass-former with Mari-Kurchan interactions
Auteur(s): Nishikawa Y., Ikeda A., Berthier L.
(Article) Publié:
The Journal Of Chemical Physics, vol. p.244503 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03807702_v1
Ref Arxiv: 2204.05130
DOI: 10.1063/5.0096356
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We numerically study the equilibrium relaxation dynamics of a two-dimensional Mari-Kurchan glass model. The tree-like structure of particle interactions forbids both non-trivial structural motifs and the emergence of a complex free-energy landscape leading to a thermodynamic glass transition, while the finite-dimensional nature of the model prevents the existence of a mode-coupling singularity. Nevertheless, the equilibrium relaxation dynamics is shown to be in excellent agreement with simulations performed in conventional glass-formers. Averaged time-correlation functions display a phenomenology typical of supercooled liquids, including the emergence of an excess signal in relaxation spectra at intermediate frequencies. We show that this evolution is accompanied by strong signatures of collective and heterogeneous dynamics which cannot be interpreted in terms of single particle hopping and emerge from dynamic facilitation. Our study demonstrates that an off-lattice interacting particle model with extremely simple structural correlations displays quantitatively realistic glassy dynamics.
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Disordered collective motion in dense assemblies of persistent particles
Auteur(s): Keta Y.-E., Jack Robert L., Berthier L.
(Article) Publié:
Physical Review Letters, vol. p.048002 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03775859_v1
Ref Arxiv: 2201.04902
DOI: 10.1103/PhysRevLett.129.048002
Ref. & Cit.: NASA ADS
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Résumé: We explore the emergence of nonequilibrium collective motion in disordered non-thermal active matter when persistent motion and crowding effects compete, using simulations of a two-dimensional model of size polydisperse self-propelled particles. In stark contrast with monodisperse systems, we find that polydispersity stabilizes a homogeneous active liquid at arbitrary large persistence times, characterized by remarkable velocity correlations and irregular turbulent flows. For all persistence values, the active fluid undergoes a nonequilibrium glass transition at large density. This is accompanied by collective motion, whose nature evolves from near-equilibrium spatially heterogeneous dynamics at small persistence, to a qualitatively different intermittent dynamics when persistence is large. This latter regime involves a complex time evolution of the correlated displacement field
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Rare events and disorder control the brittle yielding of well-annealed amorphous solids
Auteur(s): Ozawa M., Berthier L., Biroli Giulio, Tarjus Gilles
(Article) Publié:
Physical Review Research, vol. 4 p.023227 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03758384_v1
Ref Arxiv: 2102.05846
DOI: 10.1103/PhysRevResearch.4.023227
Ref. & Cit.: NASA ADS
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Résumé: We use atomistic computer simulations to provide a microscopic description of the brittle failure of amorphous materials, and we assess the role of rare events and quenched disorder. We argue that brittle yielding originates at rare soft regions, similarly to Griffiths effects in disordered systems. We numerically demonstrate how localized plastic events in such soft regions trigger macroscopic failure via the propagation of a shear band. This physical picture, which no longer holds in poorly annealed ductile materials, allows us to discuss the role of finite size effects in brittle yielding and reinforces the similarities between yielding and other disorder-controlled nonequilibrium phase transitions.
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Static self-induced heterogeneity in glass-forming liquids: Overlap as a microscope
Auteur(s): Guiselin B., Tarjus Gilles, Berthier L.
(Article) Publié:
The Journal Of Chemical Physics, vol. p.194503 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03701391_v1
Ref Arxiv: 2201.10183
DOI: 10.1063/5.0086517
Ref. & Cit.: NASA ADS
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Résumé: We propose and numerically implement a local probe of the static self-induced heterogeneity characterizing glass-forming liquids. The method relies on the equilibrium statistics of the overlap between pairs of configurations measured in mesoscopic cavities with unconstrained boundaries. By systematically changing the location of the probed cavity, we directly detect spatial variations of the overlap fluctuations. We provide a detailed analysis of the statistics of a local estimate of the configurational entropy and we infer an estimate of the surface tension between amorphous states, ingredients that are both at the basis of the random first-order transition theory of glass formation. Our results represent the first direct attempt to visualize and quantify the self-induced heterogeneity underpinning the thermodynamics of glass formation. They pave the way for the development of coarse-grained effective theories and for a direct assessment of the role of thermodynamics in the activated dynamics of deeply supercooled liquids.
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Violation of the fluctuation-dissipation theorem and effective temperatures in spin ice
Auteur(s): Raban Valentin, Berthier L., Holdsworth Peter C.W.
(Article) Publié:
-Phys.rev.b, vol. 105 p.134431 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03657988_v1
Ref INSPIRE: 2075379
DOI: 10.1103/PhysRevB.105.134431
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Résumé: We present numerical tests of the fluctuation-dissipation theorem (FDT) in the dumbbell model of spin ice with parameters suitable for dysprosium titanate. The tests are made for local spin variables, magnetic monopole density, and energy. We are able to achieve local equilibrium in which the FDT is satisfied down to below which the system completely freezes. Nonequilibrium dynamics, together with violation of the FDT, are nonetheless observed following a thermal quench into the noncontractable monopole pair regime. Despite FDT violation, an approximate linear response regime allows for the identification of effective nonequilibrium temperatures which are different for each variable. The spin variable appears hotter than the heat reservoir and the monopole concentration responds with a lower effective temperature, while the energy has a negative effective temperature. Results are discussed in the context of the monopole picture of spin ice and compared to the structure of FDT violations in other glassy materials. Prospectives for future experiments are reviewed.
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Microscopic origin of excess wings in relaxation spectra of supercooled liquids
Auteur(s): Guiselin B., Scalliet C., Berthier L.
(Article) Publié:
Nature Physics, vol. 18 p.468-+ (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03662093_v1
Ref Arxiv: 2103.01569
DOI: 10.1038/s41567-022-01508-z
WoS: WOS:000770232200001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: Glass formation is encountered in diverse materials. Experiments have revealed that dynamic relaxation spectra of supercooled liquids generically become asymmetric near the glass transition temperature, Tg, where an extended power law emerges at high frequencies. The microscopic origin of this "wing" remains unknown, and was so far inaccessible to simulations. Here, we develop a novel computational approach and study the equilibrium dynamics of model supercooled liquids near Tg. We demonstrate the emergence of a power law wing in numerical spectra, which originates from relaxation at rare, localised regions over broadly-distributed timescales. We rationalise the asymmetric shape of relaxation spectra by constructing an empirical model associating heterogeneous activated dynamics with dynamic facilitation, which are the two minimal physical ingredients revealed by our simulations. Our work offers a glimpse of the molecular motion responsible for glass formation at relevant experimental conditions.
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Relaxation dynamics in the energy landscape of glass-forming liquids
Auteur(s): Nishikawa Y., Ozawa M., Ikeda A., Chaudhuri Pinaki, Berthier L.
(Article) Publié:
Physical Review X, vol. p.021001 (2022)
Texte intégral en Openaccess :
Ref HAL: hal-03636595_v1
Ref Arxiv: 2106.01755
DOI: 10.1103/PhysRevX.12.021001
Ref. & Cit.: NASA ADS
Exporter : BibTex | endNote
Résumé: We numerically study the zero-temperature relaxation dynamics of several glass-forming models to their inherent structures, following quenches from equilibrium configurations sampled across a wide range of initial temperatures. In a mean-field Mari-Kurchan model, we find that relaxation changes from a power-law to an exponential decay below a well-defined temperature, consistent with recent findings in mean-field $p$-spin models. By contrast, for finite-dimensional systems, the relaxation is always algebraic, with a non-trivial universal exponent at high temperatures crossing over to a harmonic value at low temperatures. We demonstrate that this apparent evolution is controlled by a temperature-dependent population of localised glassy excitations. Our work unifies several recent lines of studies aiming at a detailed characterisation of the complex potential energy landscape of glass-formers, and challenges both mean-field and real space descriptions of glasses.
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