GUISELIN Benjamin
Doctorant en Contrat Doctoral avec Mission (Responsable :
BERTHIER L.)
benjamin.guiselin
umontpellier.fr
Bureau: 237, Etg: 2, Bât: 13  Site : Campus Triolet
Activités de Recherche: 
Physique/Matière Condensée/Mécanique statistique Physique/Matière Condensée/Systèmes désordonnés et réseaux de neurones Physique/Matière Condensée/Matière Molle 
Domaines de Recherche:  Physique/Matière Condensée/Mécanique statistique
 Physique/Physique/Physique Générale
 Physique/Matière Condensée/Systèmes désordonnés et réseaux de neurones
 Physique/Matière Condensée/Matière Molle
 Physique/Matière Condensée
 Physique

Productions scientifiques :


Excess wings and asymmetric relaxation spectra in a facilitated trap model
Auteur(s): Scalliet C., Guiselin B., Berthier L.
(Article) Publié:
The Journal Of Chemical Physics, vol. 155 p.064505 (2021)
Texte intégral en Openaccess :
Ref HAL: hal03355624_v1
DOI: 10.1063/5.0060408
WoS: WOS:000684667000002
Exporter : BibTex  endNote
Résumé: In a recent computer study, we have shown that the combination of spatially heterogeneous dynamics and kinetic facilitation provides a microscopic explanation for the emergence of excess wings in deeply supercooled liquids. Motivated by these findings, we construct a minimal empirical model to describe this physics and introduce dynamic facilitation in the trap model, which was initially developed to capture the thermallyactivated dynamics of glassy systems. We fully characterise the relaxation dynamics of this facilitated trap model varying the functional form of energy distributions and the strength of dynamic facilitation, combining numerical results and analytic arguments. Dynamic facilitation generically accelerates the relaxation of the deepest traps, thus making relaxation spectra strongly asymmetric, with an apparent "excess" signal at high frequencies. For wellchosen values of the parameters, the obtained spectra mimic experimental results for organic liquids displaying an excess wing. Overall, our results identify the minimal physical ingredients needed to describe excess processes in relaxation spectra of supercooled liquids.



Statistical mechanics of coupled supercooled liquids in finite dimensions
Auteur(s): Guiselin B., Berthier L., Tarjus Gilles
(Document sans référence bibliographique) Texte intégral en Openaccess :
Ref HAL: hal03245252_v1
Ref Arxiv: 2105.08946
Ref INSPIRE: 1864225
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We study the statistical mechanics of supercooled liquids when the system evolves at a temperature $T$ with a linear coupling of amplitude $\epsilon$ to its overlap with a reference configuration of the same liquid sampled at a temperature $T_0$. We use meanfield theory to fully characterize the influence of the reference temperature $T_0$, and we mainly study the case of a fixed, low$T_0$ value in computer simulations. We numerically investigate the extended phase diagram in the $(\epsilon,T)$ plane of model glassforming liquids in spatial dimensions $d=2$ and $d=3$, relying on umbrella sampling and reweighting techniques. For both $2d$ and $3d$ cases, a similar phenomenology with nontrivial thermodynamic fluctuations of the overlap is observed at low temperatures, but a detailed finitesize scaling analysis reveals qualitatively distinct behaviors. We establish the existence of a firstorder transition line for nonzero $\epsilon$ ending in a critical point in the universality class of the randomfield Ising model (RFIM) in $d=3$. In $d=2$ instead, no phase transition exists in the thermodynamic limit at finite temperatures. Our results show that glassforming liquid samples of limited size display the thermodynamic fluctuations expected for finite systems undergoing a random firstorder transition. They also establish the relevance of the physics of the RFIM for supercooled liquids, which in particular explains the qualitative difference between $2d$ and $3d$ glassformers.



Stable glassy configurations of the KobAndersen model using swap Monte Carlo
Auteur(s): Parmar A. D. S., Guiselin B., Berthier L.
(Article) Publié:
The Journal Of Chemical Physics, vol. p.134505 (2020)
Texte intégral en Openaccess :
Ref HAL: hal02986292_v1
Ref Arxiv: 2006.10377
DOI: 10.1063/5.0020208
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: The swap Monte Carlo algorithm allows the preparation of highly stable glassy configurations for a number of glassformers, but is inefficient for some models, such as the much studied binary KobAndersen (KA) mixture. We have recently developed generalisations to the KA model where swap can be very effective. Here, we show that these models can in turn be used to considerably enhance the stability of glassy configurations in the original KA model at no computational cost. We successfully develop several numerical strategies both in and out of equilibrium to achieve this goal and show how to optimise them. We provide several physical measurements indicating that the proposed algorithms considerably enhance mechanical and thermodynamic stability in the KA model, including a transition towards brittle yielding behaviour. Our results thus pave the way for future studies of stable glasses using the KA model.



Randomfield Ising model criticality in a glassforming liquid
Auteur(s): Guiselin B., Berthier L., Tarjus Gilles
(Article) Publié:
Physical Review E, vol. 102 p.042129 (2020)
Texte intégral en Openaccess :
Ref HAL: hal02925447_v1
Ref Arxiv: 2004.10555
DOI: 10.1103/PhysRevE.102.042129
WoS: WOS:000582805100002
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: We use computer simulations to investigate the extended phase diagram of a supercooled liquid linearly coupled to a quenched reference configuration. An extensive finitesize scaling analysis demonstrates the existence of a randomfield Ising model (RFIM) critical point and of a firstorder transition line, in agreement with fieldtheoretical approaches. The dynamics in the vicinity of this critical point resembles the peculiar activated scaling of RFIMlike systems, and the overlap autocorrelation displays a logarithmic stretching. Our study firmly establishes the RFIM criticality in threedimensional supercooled liquids at equilibrium.



On the overlap between configurations in glassy liquids
Auteur(s): Guiselin B., Tarjus Gilles, Berthier L.
(Article) Publié:
The Journal Of Chemical Physics, vol. 153 p.224502 (2020)
Texte intégral en Openaccess :
Ref HAL: hal02925446_v1
Ref Arxiv: 2007.07625
DOI: 10.1063/5.0022614
WoS: WOS:000600047800001
Ref. & Cit.: NASA ADS
Exporter : BibTex  endNote
Résumé: The overlap, or similarity, between liquid configurations is at the core of the meanfield description of the glass transition, and remains a useful concept when studying threedimensional glassforming liquids. In liquids, however, the overlap involves a tolerance, typically of a fraction $a/\sigma$ of the interparticle distance, associated with how precisely similar two configurations must be for belonging to the same physically relevant "state". Here, we systematically investigate the dependence of the overlap fluctuations and of the resulting phase diagram when the tolerance is varied over a large range. We show that while the location of the dynamical and thermodynamic glass transition (if present) are independent of $a/\sigma$, that of the critical point associated with a transition between a low and a highoverlap phases in the presence of an applied source nontrivially depends on the value of $a/\sigma$. We rationalize our findings by using liquidstate theory and the hypernetted chain (HNC) approximation for correlation functions. In addition, we confirm the theoretical trends by studying a threedimensional glassformer by computer simulations. We show in particular that a specific choice of $a/\sigma$ maximizes the temperature of the critical point, pushing it up in a liquid region where viscosity is low and computer investigations are easier due to a significantly faster equilibration.
