AVAILABLE SLIDES:
- Xiangyu Cao (LPENS, Paris) — Phase transitions in mean-field models of information propagation [slides]
- Hélène Delanoë-Ayari (ILM, Lyon) — Stoke’s flow experiment in biological tissues: comparison with an active abiotic system [slides]
- Gianfranco Durin (INRIM, Torino) — Earthquake-like dynamics of magnetic domain walls in ultrathin films [slides]
- Pierre-Antoine Geslin (INSA, Lyon) — Dislocation depinning in concentrated random alloys [slides]
- Edmond Orignac (LPENS, Lyon) — Quantum Systems [slides]
Xiangyu Cao (LPENS, Paris) — Phase transitions in mean-field models of information propagation [slides]
Many-body systems (both quantum and classical) can thermalise under their intrinsic dynamics. The modern understanding of how this happens is information theoretical: Interaction “scrambles” the information of an initial perturbation, making it effectively inaccessible to a late time observer. A notable exception to this generic picture is the case of detectors, which are many-body systems designed to amplify the injected information (to be detected) and make it available to many observers.
I will report recent works aiming at understanding the two above behaviours as “dynamical phases of information”, separated by phase transition(s).
Based on the publications:
Phys. Rev. Lett. 132, 110201 (2024)
Phys. Rev. A 109, 032226 (2024)
and ongoing work.
Hélène Delanoë-Ayari (ILM, Lyon) — Stoke’s flow experiment in biological tissues: comparison with an active abiotic system [slides]
What is common between an assembly of motile cells whose movement is fueled by ATP and active colloids able to move using some chemical reactions? This is the question we are addressing using a rheological setup that allows us to probe the mechanical properties of these systems. We have designed a stokes experiment on both cells and colloids, and by analyzing the highly heterogeneous flow that is triggered, we hope to better understand the analogies between these systems and especially the role of activity, which can be easily controlled in case of the colloidal system.
Gianfranco Durin (INRIM, Torino) — Earthquake-like dynamics of magnetic domain walls in ultrathin films [slides]
In ultrathin magnetic film with perpendicular magnetic anisotropy, the magnetization reversal often occurs by nucleation and growth of little bubbles. At tiny magnetic fields, these bubbles show a very slow growth, those contours, i.e. the domain walls, creep only via thermal activation over the pinning centers present in the sample. This creep dynamics is highly intermittent and correlated. A localized instability triggers a cascade, akin to aftershocks following a large earthquake, where the pinned wall undergoes large reorganizations in a compact active region for a few seconds. Surprisingly, the size and shape of these reorganizations display the same scale-free statistics of the depinning avalanches in agreement with the quenched Kardar-Parisi-Zhang universality class.
Pierre-Antoine Geslin (INSA, Lyon) — Dislocation depinning in concentrated random alloys [slides]
Dislocations are linear defects whose mobility controls the mechanical properties of metals. Alloying provides a common strategy to strengthen metallic materials, as solute atoms distributed in the system act as obstacles to dislocation motion. The interaction of a dislocation line with a random distribution of solutes can be seen as the pinning of an elastic line in a random environment, a situation that has been extensively studied in statistical physics. As the nature of the noise is important to characterize the problem and the corresponding universality class, we first develop an elastic model of random alloys where atoms of different natures are modeled as Eshelby inclusions embedded in an isotropic elastic medium. This allows us to derive analytical expressions for the variance [1] of the elastic fields (displacements, strains, stresses) as well as their spatial correlations [2]. In particular, we show that spatial correlations of the stress field pinning dislocations are highly anisotropic and vary with the character of the dislocation (screw or edge) [2,3]. The second step consists in investigating the behavior of dislocation lines in such a correlated environment. In particular, we show that, at the depinning threshold, edge dislocations follow the classical quenched Kardar-Parisi-Zhang (qKPZ) universality class. On the other hand, the behavior of the screw dislocation is significantly different and falls into the negative qKPZ universality class discussed in the literature [4]. These different behaviors find their origin in the anisotropic nature of the underlying pinning field.
[1] P.-A. Geslin and D. Rodney. J. Mech. Phys. Sol. 153, 104479 (2021).
[2] P.-A. Geslin, A. Rida, and D. Rodney. J. Mech. Phys. Sol. 153, 104480 (2021).
[3] A. Rida, E. Martinez, D. Rodney, P.-A. Geslin. Phys. Rev. Mater. 6, 033605 (2022).
[4] S. Atis, A.K. Dubey, D. Salin, L. Talon, P. Le Doussal, and K.J. Wiese, Phys. Rev. Lett. 114, 234502 (2015).
Martin Lenz (LPTMS, Paris-Saclay) & Olivia du Roure (PMMH, Paris) — Elasticity from entanglements in branched actin
The biologically crucial elasticity of actin networks is usually understood as an interplay between the bending and stretching of its filaments. This point of view however fails when applied to the weakly coordinated branched actin networks found at the leading edge of the cell. Through experiments and theory, we show that their elasticity crucially involves reversible contacts between their filaments. These contacts can in turn be controlled through filament entanglement during network growth to regulate the final properties of the network. These properties could be key to understanding how moving cells dynamically adapt their cytoskeleton to their environment.
Edmond Orignac (LPENS, Lyon) — Quantum Systems [slides]
I will review the mapping of elastic quantum systems in d dimensions with point disorder to classical disordered systems in (d+1) dimensions with columnar disorder. I will discuss the case in one dimension and its relation with Anderson Localization of interacting particles. I will then turn to the two dimensional case and to the Wigner crystal.
Aleksandra Petković (LPT, Toulouse) — Casimir-like effect in one-dimensional quantum liquids
The concept of mediated interactions plays a pivotal role in physics. It refers to an effective interaction between external objects placed in a fluctuating medium. Its range depends on the details of correlations in the medium. The famous example is given by the Casimir effect that denotes the attraction between two large neutral conducting plates placed in a vacuum. I will discuss the fluctuation-induced interaction between impurities in one- dimensional quantum liquids.
François Petrelis (LPENS, Paris) — Earthquake statistical properties: an explanation for the distribution of magnitude and for the existence of aftershocks
Earthquakes in nature follow several statistical properties. In particular, the distribution of energy released by an earthquake (Gutenberg-Richter's law) and the frequency of aftershocks after a large event (Omori's law) are both power-laws. By studying several earthquake models, we have shown that the Gutenberg-Richter law results from the spatial distribution of the stress field. This field is self-similar at large scale and for two dimensionnal systems can be modelled as a random surface. Using this analogy, a series of predictions is made that includes the Gutenberg-Richter law and the value of its exponent (so called b-value) together with the existence of aftershocks and their temporal distribution following Omori's law.
Beatrice Ruta (Néel, Grenoble) — Structure and Atomic motion in metallic glasses at high pressure
Despite metallic glasses are among the most studied metallic materials, still very little is known on the evolution of their unique structural, dynamical and elastic properties under compression, owing to the difficulty to perform in-situ high pressure experiments. Coupling the brightest x-rays available in synchrotrons with cutting edge high pressure technologies, we provide direct evidence of the microscopic structural and dynamical physical mechanisms occurring under in-situ high pressure compression and decompression in the GPa range, from the onset of the perturbation up to a severely-deformed state. We show that while pressure promotes density increasing through quasi-elastic structural deformations, the atomic mobility exhibits a hysteresis and is enhanced up to a factor 15 even at temperatures well below the glass transition. This surprising behaviour results from a competition between fast avalanche-like atomic rearrangements and slow relaxation processes triggered by an anomalous super-diffusive collective particle displacement. These results provide new insights on the effect of deformation in non-ergodic materials and support the occurrence of string-like diffusion of liquid-like atoms in metallic glasses.
Valérie Vidal (ENS Lyon) — Emergence of instabilities during fluid migration in sedimentary layers
Although multiphase flows are ubiquitous in natural and industrial systems, the comprehension of the physical mechanisms at stake is still a challenge. In particular, the link between the processes at the microscale - grain size, shape, asperities - and the behavior at larger scale (particle suspension, transport, emergence of instabilities...) remains unknown. Based on laboratory experiments, we investigate the dynamics of an immersed granular layer submitted to a localized fluid injection. A suspension results from the competition between particle entrainment and sedimentation. In a given range of parameters and for different experimental configurations, the system exhibits puzzling instabilities such as self-induced oscillations or periodic fluidization patterns. The importance of such phenomena will be discussed in regards to geophysical and environmental applications.
