Alexis Poncet
Laboratoire de Physique, ENS Lyon, France

“Collective effects in driven matter: from one-dimensional crowding to 2D melting”

The theoretical description of the structure and dynamics of matter far from thermal equilibrium is at the heart of modern statistical physics.
In this seminar, I will focus on two prototypical examples of interacting agents driven out of equilibrium: driven hard-core particles confined in 1D geometries, and 2D colloidal crystals whose the elementary units are activated, either by torques or forces. The first example will be discussed from a fundamental perspective combining analytical theory and extensive numerical simulations, the second example will be discussed combing experiments, simulations and theory.

In the first part of my talk I will address some fundamental questions about the response of non-equilibrium matter to point forces far beyond linear response theory. To tackle this formidable challenge, I will focus on the dynamic response of single-file systems locally driven by intruders. While at high density intruders can only follow one another, at low density they can unbind and separate. To explain this unbinding transition [1], I will introduce a hydrodynamic description of the density field. Strikingly, such an approach can be extended to all orders of displacement-density correlations [2], proving a complete characterization of the one-tag process in single-file lattices closely related to their integrability.

In the second part of my talk, I will describe two seemingly unrelated experiments where spinning particles [3] and confined emulsions form highly dynamical polycrystals kneaded by the constant reconfigurations of grains boundaries. I will show that in both cases the lively dynamics of the crystal originate from hydrodynamic interactions that violate Newton’s third law. I will investigate the impact of non-reciprocity on stabilized crystalline phases [4]. In particular I will show that non-reciprocal interactions propel the topological defects of crystals thereby suppressing long-range order and giving rise to intrinsically dynamical polycrystalline phases.

[1] Bénichou, Démery & Poncet; Phys. Rev. Lett. 120, 070601 (2018)
[2] Poncet, Grabsch, Illien & Bénichou; Phys. Rev. Lett. 127, 220601 (2021)
[3] Bililign, Usabiaga, Ganan, Poncet, Soni, Magkiriadou, Shelley, Bartolo & Irvine; Nat. Phys. 18, 212–218 (2021)
[4] Poncet & Bartolo; Phys. Rev. Lett. 128, 048002 (2022)

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