Bulletin of the American Physical Society
APS March Meeting 2022
Volume 67, Number 3
Monday–Friday, March 14–18, 2022; Chicago
Session M14: Non-Reciprocity in Soft and Active MatterInvited Live Streamed
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Sponsoring Units: DSOFT Chair: Daniel Sussman, Emory University Room: McCormick Place W-183B |
Wednesday, March 16, 2022 8:00AM - 8:36AM |
M14.00001: Predator–prey interactions between droplets driven by non-reciprocal oil exchange Invited Speaker: Lauren Zarzar |
Wednesday, March 16, 2022 8:36AM - 9:12AM |
M14.00002: Non-reciprocal phase transitions Invited Speaker: Michel Fruchart Out of equilibrium, a lack of reciprocity is the rule rather than the exception. Non-reciprocity occurs, for instance, in active matter, non-equilibrium systems, networks of neurons, social groups with conformist and contrarian members, directional interface growth phenomena and metamaterials. Although wave propagation in non-reciprocal media has recently been closely studied, less is known about the consequences of non-reciprocity on the collective behaviour of many-body systems. Here we show that non-reciprocity leads to time-dependent phases in which spontaneously broken continuous symmetries are dynamically restored. We illustrate this mechanism with simple robotic demonstrations. The resulting phase transitions are controlled by spectral singularities called exceptional points. We describe the emergence of these phases using insights from bifurcation theory and non-Hermitian quantum mechanics. Our approach captures non-reciprocal generalizations of three archetypal classes of self-organization out of equilibrium: synchronization, flocking and pattern formation. Collective phenomena in these systems range from active time-(quasi)crystals to exceptional-point-enforced pattern formation and hysteresis. Our work lays the foundation for a general theory of critical phenomena in systems whose dynamics is not governed by an optimization principle. |
Wednesday, March 16, 2022 9:12AM - 9:48AM |
M14.00003: Irreversibility, heat and information flows induced by non-reciprocal interactions Invited Speaker: Sarah Loos In recent years, much progress was made in understanding the fundamental principles governing living and artificial complex systems that naturally operate far from thermal equilibrium. However, so far, little attention has been paid to the implications of nonreciprocal interactions, which cannot be represented by interaction Hamiltonians, contrasting all interactions traditionally considered in statistical mechanics and thermodynamics. Such interactions emerge commonly in biological, chemical and feedback systems, and are widespread in active matter. They further have applications in (quantum) engineering, and are experimentally realised in colloidal systems. In this talk, I will use simple time- and space-continuous Langevin models to discuss the fundamental thermodynamic implications of nonreciprocity [1], employing concepts from stochastic thermodynamics and information theory. In particular, under fairly general conditions, nonreciprocal coupling implies a steady energy flow through the system, which is necessarily accompanied by an information flow. The entropy balance of an individual nonreciprocally coupled subsystem contains an information-theoretical contribution, giving rise to a generalised second law like the ones known for systems under the influence of external feedback control. Remarkably, nonreciprocal coupling can induce an anomalous heat flow from cold to hot, somewhat resembling the effect of an 'Maxwell demon'. Nonreciprocal interactions can further be used to engineer nontrivial memory [2]. Lastly, we also consider the impact of nonreciprocal coupling on collective behaviour and show that it can induce long-range order. |
Wednesday, March 16, 2022 9:48AM - 10:24AM |
M14.00004: Nonreciprocity as a generic route to traveling and oscillatory states Invited Speaker: Zhihong You Time periodic patterns occur ubiquitously in nature. Most mathematical models that capture such spatiotemporal dynamics, including reaction–diffusion equations, excitable systems, and prey–predator equations, are unified by the fact that the dynamical variables are nonconserved fields. Here, we demonstrate that traveling and oscillatory patterns can arise in multicomponent systems described by purely diffusive conserved fields from nonreciprocal interactions between species. The appearance of time periodic states in a purely diffusive system with no apparent external forcing is unexpected and defies intuition. Our work suggests that nonreciprocity provides a generic mechanism for the establishment of time periodic states, which might be relevant to both biological systems and synthetic systems with nonreciprocal effective interactions mediated by non-equilibrium environments, such as mixtures of active colloids. |
Wednesday, March 16, 2022 10:24AM - 11:00AM |
M14.00005: Non-reciprocity in quasi-two-dimensional complex plasmas Invited Speaker: Alexei Ivlev Complex plasmas, which are composed of a weakly ionized gas and charged microparticles, represent the plasma state of soft matter. Along with colloidal dispersions, they have been widely used as a natural model system of various generic phenomena occurring in liquids and solids. The dynamics of individual microparticles in experiments with quasi-two-dimensional (q2D) complex plasmas levitating above a horizontal electrode can be easily visualized and measured. These systems have two remarkable features distinguishing them from other soft-matter systems. First, since the surrounding gas is dilute, the short-time dynamics of individual microparticles in strongly coupled complex plasmas is practically undamped. Second, the effective interparticle interactions in q2D complex plasmas violate the action-reaction symmetry: the vertical electric field near the electrode induces a plasma flow, which generates plasma wakes around the levitating microparticles and thus makes their effective electrostatic interactions nonreciprocal. |
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