Publications (123)463.06 Total impact
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ABSTRACT: We develop a theory of amorphous interfaces in glassforming liquids. We show that the statistical properties of these surfaces, which separate regions characterized by different amorphous arrangements of particles, coincide with the ones of domain walls in the random field Ising model. A major consequence of our results is that supercooled liquids are characterized by two different static lengths: the pointtoset $\xi_{PS}$ which is a measure of the spatial extent of cooperative rearranging regions and the wandering length $\xi_\perp$ which is related to the fluctuations of their shape. We find that $\xi_\perp$ grows when approaching the glass transition but slower than $\xi_{PS}$. The wandering length increases as $s_c^{1/2}$, where $s_c$ is the configurational entropy. Our results strengthen the relationship with the random field Ising model found in recent works. They are in agreement with previous numerical studies of amorphous interfaces and provide a theoretical framework for explaining numerical and experimental findings on pinned particle systems and static lengths in glassforming liquids.11/2014;  [Show abstract] [Hide abstract]
ABSTRACT: We analyse, using Inhomogenous ModeCoupling Theory, the critical scaling behaviour of the dynamical susceptibility at a distance epsilon from continuous secondorder glass transitions. We find that the dynamical correlation length xi behaves generically as epsilon^{1/3} and that the upper critical dimension is equal to six. More surprisingly, we find activated dynamic scaling, where xi grows with time as [ln(t)]^2 exactly at criticality. All these results suggest a deep analogy between the glassy behaviour of attractive colloids or randomly pinned supercooled liquids and that of the Random Field Ising Model.Physical Review Letters 01/2014; 113(24). · 7.73 Impact Factor  Physics 11/2013; 6.
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ABSTRACT: The dramatic dynamic slowing down associated with the glass transition is considered by many to be related to the existence of a static length scale that grows when temperature decreases. Defining, identifying, and measuring such a length is a subtle problem. Recently, two proposals, based on very different insights regarding the relevant physics, were put forward. One approach is based on the pointtoset correlation technique and the other on the scale where the lowest eigenvalue of the Hessian matrix becomes sensitive to disorder. Here we present numerical evidence that the two approaches might result in the same identical length scale. This provides mutual support for their relevance and, at the same time, raises interesting theoretical questions, discussed in the conclusion.Physical Review Letters 10/2013; 111(16):165701. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We introduce an approach to derive an effective scalar field theory for the glass transition; the fluctuating field is the overlap between equilibrium configurations. We apply it to the case of constrained liquids for which the introduction of a conjugate source to the overlap field was predicted to lead to an equilibrium critical point. We show that the longdistance physics in the vicinity of this critical point is in the same universality class as that of a paradigmatic disordered model: the randomfield Ising model. The quenched disorder is provided here by a reference equilibrium liquid configuration. We discuss to what extent this fieldtheoretical description and the mapping to the random field Ising model hold in the whole supercooled liquid regime, in particular near the glass transition.Physical Review Letters 09/2013; 112(17). · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In this work, we numerically investigate a new method for the characterization of growing length scales associated with spatially heterogeneous dynamics of glassforming liquids. This approach, motivated by the formulation of the inhomogeneous modecoupling theory (IMCT) [Biroli, G.; et al. Phys. Rev. Lett. 2006 97, 195701], utilizes inhomogeneous molecular dynamics simulations in which the system is perturbed by a spatially modulated external potential. We show that the response of the twopoint correlation function to the external field allows one to probe dynamic correlations. We examine the critical properties shown by this function, in particular, the associated dynamic correlation length, that is found to be comparable to the one extracted from standardly employed fourpoint correlation functions. Our numerical results are in qualitative agreement with IMCT predictions but suggest that one has to take into account fluctuations not included in this meanfield approach to reach quantitative agreement. Advantages of our approach over the more conventional one based on fourpoint correlation functions are discussed.The Journal of Physical Chemistry B 07/2013; · 3.38 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the effect of confinement on glassy liquids using Random First Order Transition theory as framework. We show that the characteristic lengthscale above which confinement effects become negligible is related to the pointtoset lengthscale introduced to measure the spatial extent of amorphous order in supercooled liquids. By confining below this characteristic size, the system becomes a glass. Eventually, for very small sizes, the effect of the boundary is so strong that any collective glassy behavior is wiped out. We clarify similarities and differences between the physical behaviors induced by confinement and by pinning particles outside a spherical cavity (the protocol introduced to measure the pointtoset length). Finally, we discuss possible numerical and experimental tests of our predictions.Physical Review Letters 05/2013; 111(10). · 7.73 Impact Factor 
Article: Random pinning glass transition: Hallmarks, meanfield theory and renormalization group analysis.
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ABSTRACT: We present a detailed analysis of glass transitions induced by pinning particles at random from an equilibrium configuration. We first develop a meanfield analysis based on the study of pspin spherical disordered models and then obtain the threedimensional critical behavior by the MigdalKadanoff real space renormalization group method. We unveil the important physical differences with the case in which particles are pinned from a random (or very high temperature) configuration. We contrast the pinning particles approach to the ones based on biasing dynamical trajectories with respect to their activity and on coupling to equilibrium configurations. Finally, we discuss numerical and experimental tests.The Journal of Chemical Physics 03/2013; 138(12):12A547. · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We characterize vibrational motion occurring at low temperatures in dense suspensions of soft repulsive spheres over a broad range of volume fractions encompassing the jamming transition at (T = 0, ϕ = ϕJ). We find that characteristic time and length scales of thermal vibrations obey critical scaling in the vicinity of the jamming transition. We show in particular that the amplitude and the time scale of dynamic fluctuations diverge symmetrically on both sides of the transition, and directly reveal a diverging correlation length. The critical region near ϕJ is divided in three different regimes separated by a characteristic temperature scale T(⋆)(ϕ) that vanishes quadratically with the distance to ϕJ. While two of them, (T < T(⋆)(ϕ), ϕ > ϕJ) and (T < T(⋆)(ϕ), ϕ < ϕJ), are described by harmonic theories developed in the zero temperature limit, the third one for T > T(⋆)(ϕ) is inherently anharmonic and displays new critical properties. We find that the quadratic scaling of T(⋆)(ϕ) is due to nonperturbative anharmonic contributions, its amplitude being orders of magnitude smaller than the perturbative prediction based on the expansion to quartic order in the interactions. Our results show that thermal vibrations in colloidal assemblies directly reveal the critical nature of the jamming transition. The critical region, however, is very narrow and has not yet been attained experimentally, even in recent specificallydedicated experiments.The Journal of Chemical Physics 03/2013; 138(12):12A507. · 3.12 Impact Factor 
Article: Perspective: The glass transition.
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ABSTRACT: We provide here a brief perspective on the glass transition field. It is an assessment, written from the point of view of theory, of where the field is and where it seems to be heading. We first give an overview of the main phenomenological characteristics, or "stylised facts," of the glass transition problem, i.e., the central observations that a theory of the physics of glass formation should aim to explain in a unified manner. We describe recent developments, with a particular focus on real space properties, including dynamical heterogeneity and facilitation, the search for underlying spatial or structural correlations, and the relation between the thermal glass transition and athermal jamming. We then discuss briefly how competing theories of the glass transition have adapted and evolved to account for such real space issues. We consider in detail two conceptual and methodological approaches put forward recently, that aim to access the fundamental critical phenomenon underlying the glass transition, be it thermodynamic or dynamic in origin, by means of biasing of ensembles, of configurations in the thermodynamic case, or of trajectories in the dynamic case. We end with a short outlook.The Journal of Chemical Physics 03/2013; 138(12):12A301. · 3.12 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We give an overview of our recent works in which the a.c. nonlinear dielectric response of an archetypical glassformer (glycerol) was measured close to its glass transition temperature T g . The purpose was to investigate the prediction that the nonlinear susceptibility is directly related to the number of dynamically correlated molecules N { corr} (T). We explain that two nonlinear susceptibilities are available, namely χ3 (3) and χ3 (1), which correspond respectively to the nonlinear cubic response at the third harmonics and at the first harmonics. We describe how to measure these nonlinear responses, even if they yield signals much smaller than that of the linear response. We show that both \vert {χ }3^{(3)}(ω,T)\vert and \vert {χ }3^{(1)}(ω,T)\vert are peaked as a function of the angular frequency ω and mainly obeys critical scaling as a function of ωτα(T), where τα(T) is the relaxation time of the liquid. Both χ3 (3) and χ3 (1) decay with the same powerlaw of ω beyond the peak. The height of the peak increases as the temperature approaches T g : This yields an accurate determination of the temperature dependence of N { corr} (T), once the contribution of saturation of dipoles is disentangled from that of dynamical glassy correlations.01/2013; 
Article: Difference between level statistics, ergodicity and localization transitions on the Bethe lattice
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ABSTRACT: We show that noninteracting disordered electrons on a Bethe lattice display a new intermediate phase which is delocalized but nonergodic, i.e. it is characterized by Poisson instead of GOE statistics. The physical signature of this phase is a very heterogenous transport that proceeds over a few disorder dependent paths only. We show that the transition to the usual ergodic delocalized phase, which takes place for a disorder strength smaller than the one leading to the localization transition, is related to the freezingglass transition of directed polymers in random media. The numerical study of level and eigenstate statistics, and of the singular properties of the probability distribution of the local density of states all support the existence of this new intermediate phase. Our results suggest that the localization transition may change nature in high dimensional systems.11/2012;  [Show abstract] [Hide abstract]
ABSTRACT: Several meanfield computations have revealed the existence of an out of equilibrium dynamical transition induced by quantum quenching an isolated system starting from its symmetry broken phase. In this work we focus on the quantum phi^4 Ncomponent field theory. By taking into account dynamical fluctuations at the HartreeFock level, corresponding to the leading order of the 1/N expansion, we derive the critical properties of the dynamical transition beyond meanfield theory (including at finite temperature). We find diverging time and lengthscales, dynamic scaling and aging. Finally, we unveil a relationship with coarsening, an offequilibrium dynamical regime that can be induced by quenching from the symmetric toward the symmetry broken phase.Physical Review B 11/2012; · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We have measured, as a function of the age t_{a}, the aging of the nonlinear dielectric susceptibility χ_{3} of glycerol below the glass transition. Whereas the linear susceptibility can be accurately accounted for in terms of an age dependent relaxation time τ_{α}(t_{a}), this scaling breaks down for χ_{3}, suggesting an increase of the amplitude of χ_{3}. This is a strong indication that the number N_{corr} of molecules involved in relaxation events increases with t_{a}. For T=0.96×T_{g}, we find that N_{corr} increases by ∼10% when t_{a} varies from 1 to 100 ks. This sheds new light on the relation between length scales and time scales in glasses.Physical Review Letters 10/2012; 109(17):175702. · 7.73 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: At the meanfield level, on fully connected lattices, several disordered spin models have been shown to belong to the universality class of "structural glasses", with a "random firstorder transition" (RFOT) characterized by a discontinuous jump of the order parameter and no latent heat. However, their behavior in finite dimensions is often drastically different, displaying either no glassiness at all or a conventional spinglass transition. We clarify the physical reasons for this phenomenon and stress the unusual fragility of the RFOT to shortrange fluctuations, associated e.g. with the mere existence of a finite number of neighbors. Accordingly, the solution of fully connected models is only predictive in very high dimension whereas, despite being also meanfield in character, the Bethe approximation provides valuable information on the behavior of finitedimensional systems. We suggest that before embarking on a fullblown account of fluctuations on all scales through computer simulation or renormalizationgroup approach, models for structural glasses should first be tested for the effect of shortrange fluctuations and we discuss ways to do it. Our results indicate that disordered spin models do not appear to pass the test and are therefore questionable models for investigating the glass transition in three dimensions. This also highlights how nontrivial is the first step of deriving an effective theory for the RFOT phenomenology from a rigorous integration over the shortrange fluctuations.Physical review. B, Condensed matter 10/2012; 87(6). · 3.66 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We present a comprehensive theoretical study of finitesize effects in the relaxation dynamics of glassforming liquids. Our analysis is motivated by recent theoretical progress regarding the understanding of relevant correlation length scales in liquids approaching the glass transition. We obtain predictions both from general theoretical arguments and from a variety of specific perspectives: modecoupling theory, kinetically constrained and defect models, and random firstorder transition theory. In the last approach, we predict in particular a nonmonotonic evolution of finitesize effects across the modecoupling crossover due to the competition between modecoupling and activated relaxation. We study the role of competing relaxation mechanisms in giving rise to nonmonotonic finitesize effects by devising a kinetically constrained model where the proximity to the modecoupling singularity can be continuously tuned by changing the lattice topology. We use our theoretical findings to interpret the results of extensive molecular dynamics studies of four model liquids with distinct structures and kinetic fragilities. While the less fragile model only displays modest finitesize effects, we find a more significant size dependence evolving with temperature for more fragile models, such as LennardJones particles and soft spheres. Finally, for a binary mixture of harmonic spheres we observe the predicted nonmonotonic temperature evolution of finitesize effects near the fitted modecoupling singularity, suggesting that the crossover from modecoupling to activated dynamics is more pronounced for this model. Finally, we discuss the close connection between our results and the recent report of a nonmonotonic temperature evolution of a dynamic length scale near the modecoupling crossover in harmonic spheres.Physical Review E 09/2012; 86(31):031502. · 2.31 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We study the effect of freezing the positions of a fraction c of particles from an equilibrium configuration of a supercooled liquid at a temperature T. We show that within the random firstorder transition theory pinning particles leads to an ideal glass transition for a critical fraction c = c(K)(T) even for moderate supercooling; e.g., close to the ModeCoupling transition temperature. First we derive the phase diagram in the T  c plane by mean field approximations. Then, by applying a realspace renormalization group method, we obtain the critical properties for c  c(K)(T) → 0, in particular the divergence of length and time scales, which are dominated by two zerotemperature fixed points. We also show that for c = c(K)(T) the typical distance between frozen particles is related to the static pointtoset length scale of the unconstrained liquid. We discuss what are the main differences when particles are frozen in other geometries and not from an equilibrium configuration. Finally, we explain why the glass transition induced by freezing particles provides a new and very promising avenue of research to probe the glassy state and ascertain, or disprove, the validity of the theories of the glass transition.Proceedings of the National Academy of Sciences 06/2012; 109(23):88505. · 9.81 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: In this work we provide a comprehensive analysis of the activation problem out of equilibrium. We generalize the Arrhenius law for systems driven by non conservative time independent forces, subjected to retarded friction and nonMarkovian noise. The role of the energy function is now played by the out of equilibrium potential {\phi} = lim_{T{\to}0} T log P_s, with P_s being the steady state probability distribution and T the strength of the noise. We unveil the relationship between the generalized Arrhenius law and a timereversal transformation discussed in the context of fluctuations theorems out of equilibrium. Moreover, we characterize the noiseactivated trajectories by obtaining their explicit expressions and identifying their irreversible nature. Finally, we discuss a real biological application that illustrates our results.04/2012;  [Show abstract] [Hide abstract]
ABSTRACT: The intestinal microbiota plays important roles in digestion and resistance against enteropathogens. As with other ecosystems, its species composition is resilient against small disturbances but strong perturbations such as antibiotics can affect the consortium dramatically. Antibiotic cessation does not necessarily restore pretreatment conditions and disturbed microbiota are often susceptible to pathogen invasion. Here we propose a mathematical model to explain how antibioticmediated switches in the microbiota composition can result from simple social interactions between antibiotictolerant and antibioticsensitive bacterial groups. We build a twospecies (e.g. two functionalgroups) model and identify regions of domination by antibioticsensitive or antibiotictolerant bacteria, as well as a region of multistability where domination by either group is possible. Using a new framework that we derived from statistical physics, we calculate the duration of each microbiota composition state. This is shown to depend on the balance between random fluctuations in the bacterial densities and the strength of microbial interactions. The singular value decomposition of recent metagenomic data confirms our assumption of grouping microbes as antibiotictolerant or antibioticsensitive in response to a single antibiotic. Our methodology can be extended to multiple bacterial groups and thus it provides an ecological formalism to help interpret the present surge in microbiome data.PLoS Computational Biology 04/2012; 8(4):e1002497. · 4.83 Impact Factor  [Show abstract] [Hide abstract]
ABSTRACT: We obtain the patchrepetition entropy Sigma within the Random First Order Transition theory (RFOT) and for the square plaquette system, a model related to the dynamical facilitation theory of glassy dynamics. We find that in both cases the entropy of patches of linear size l, Sigma(l), scales as s_c l^d+A l^{d1} down to lengthscales of the order of one, where A is a positive constant, s_c is the configurational entropy density and d the spatial dimension. In consequence, the only meaningful length that can be defined from patchrepetition is the crossover length xi=A/s_c. We relate xi to the typical lengthscales already discussed in the literature and show that it is always of the order of the largest static length. Our results provide new insights, which are particularly relevant for RFOT theory, on the possible real space structure of supercooled liquids. They suggest that this structure differs from a mosaic of different patches having roughly the same size.EPL (Europhysics Letters) 01/2012; 98(3). · 2.27 Impact Factor
Publication Stats
4k  Citations  
463.06  Total Impact Points  
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Institutions

2011–2012

Atomic Energy and Alternative Energies Commission
 Institut de Physique Théorique (IPhT)
GifsurYvette, IledeFrance, France


2005–2012

Cea Leti
Grenoble, RhôneAlpes, France


2009

Pierre and Marie Curie University  Paris 6
 Laboratoire de Physique Théorique et des Hautes Energies (LPTHE)
Paris, IledeFrance, France


1999–2008

French National Centre for Scientific Research
 • Laboratoire Charles Coulomb
 • Laboratoire Statistique et Génome
Lutetia Parisorum, ÎledeFrance, France


2007

Université de Montpellier 1
Montpelhièr, LanguedocRoussillon, France


2001–2006

Ecole Normale Supérieure de Paris
 Laboratoire de Physique Théorique
Paris, IledeFrance, France


2004

Sapienza University of Rome
 Department of Physics
Roma, Latium, Italy


2002

Université ParisSud 11
 Laboratoire de Physique Théorique et Modèles Statistiques
Orsay, ÎledeFrance, France


2001–2002

Rutgers, The State University of New Jersey
 Department Physics and Astronomy
New Brunswick, New Jersey, United States
