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Ref Arxiv: 1507.04120
DOI: 10.1103/PhysRevE.94.022615
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44 Citations
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We use computer simulations to analyse the yielding transition during large-amplitude oscillatory shear of a simple model for soft jammed solids. Simultaneous analysis of global mechanical response and particle-scale motion demonstrates that macroscopic yielding, revealed by a smooth crossover in mechanical properties, is accompanied by a sudden change in the particle dynamics, which evolves from non-diffusive motion to irreversible diffusion as the amplitude of the shear is increased. We provide numerical evidence that this sharp change corresponds to a non-equilibrium first-order dynamic phase transition, thus establishing the existence of a well-defined microscopic dynamic signature of the yielding transition in amorphous materials in oscillatory shear.

Commentaires: 7 pages, 4 figures, Phys. Rev. E (in press). Réf Journal: Phys. Rev. E 94, 022615 (2016)

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Ref Arxiv: 1511.04201
DOI: 10.1073/pnas.1607730113
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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)

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Ref Arxiv: 1604.05532
DOI: 10.1063/1.4959034
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7 Citations
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We employ a field-theoretical variational approach to study the behavior of ionic solutions in the grand canonical ensemble. To describe properly the hardcore interactions between ions, we use a cutoff in Fourier space for the electrostatic contribution of the grand potential and the Carnahan-Starling equation of state with a modified chemical potential for the pressure one. We first calibrate our method by comparing its predictions at room temperature with Monte Carlo results for excess chemical potential and energy. We then validate our approach in the bulk phase by describing the classical “ionic liquid-vapor” phase transition induced by ionic correlations at low temperature, before applying it to electrolytes at room temperature confined to nanopores embedded in a low dielectric medium and coupled to an external reservoir of ions. The ionic concentration in the nanopore is then correctly described from very low bulk concentrations, where dielectric exclusion shifts the transition up to room temperature for sufficiently tight nanopores, to high concentrations where hardcore interactions dominate which, as expected, modify only slightly this ionic “capillary evaporation.”

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Ref Arxiv: 1602.07524
DOI: 10.1103/PhysRevLett.116.176801
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39 Citations
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By numerical simulations and analytical studies, we show that the phenomenon of microwave-induced resistance oscillations can be understood as a classical memory effect caused by re-collisions of electrons with scattering centers after a cyclotron period. We develop a Drude-like approach to magneto-transport in presence of a microwave field, taking account of memory effects, and find an excellent agreement between numerical and analytical results, as well as a qualitative agreement with experiment.

Commentaires: 6 pages, 3 figures. Réf Journal: Phys. Rev. Lett. 116, 176801 (2016)

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I will review our recent experiments revisiting the optical properties of G centers in silicon.

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Ref Arxiv: 1603.05017
DOI: 10.1063/1.4954327
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10 Citations
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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)

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The dynamics of glass-forming liquids is heterogeneous and displays growing spatial correlations upon cooling. Whether such behavior arises from fluctuations in local structure or more complex forms of amorphous order is a highly debated question. To clarify this issue, we studied several model liquids within a coherent simulation framework based on the iso-configurational ensemble [1]. We found that the correlation between the preferred local structure and dynamic heterogeneity is system-dependent: it is pronounced in systems that deviate markedly from the mean-field picture of glassy dynamics and weak or absent in models that adhere to it to a good extent. I will review these results and then assess recent proposals to account for dynamic fluctuations using more genericmeasures of structure, such as overlap distributions and predictability analysis. Finally, I will characterize the structure of ultra-stable glassy samples of hard and soft spheres, which we recently equilibrated at large packing fractions using an optimized swap Monte Carlo algorithm [2]. [1] G. M. Hocky, D. Coslovich, A. Ikeda, D. R. Reichman, Phys. Rev. Lett. 113, 157801 (2014)[2] L. Berthier, D. Coslovich, A. Ninarello, M. Ozawa, arXiv:1511.06182 (2015)