Bulletin of the American Physical Society
APS March Meeting 2023
Volume 68, Number 3
Las Vegas, Nevada (March 5-10)
Virtual (March 20-22); Time Zone: Pacific Time
Session F07: Non-reciprocity in Soft and Active Matter II |
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Sponsoring Units: DSOFT GSNP Chair: Anton Souslov, University of Bath; Daniel Sussman, Emory University Room: Room 130 |
Tuesday, March 7, 2023 8:00AM - 8:12AM |
F07.00001: Non-reciprocal frustration induced order-by-disorder and spin-glass-like state Ryo Hanai In this talk, I will draw an unexpected link between two concepts that, at a glance, do not seem to have anything to do with each other: geometrical frustration and non-reciprocal interactions [1]. I show that exotic phenomena that are known to occur in systems with the former can also occur in the latter. |
Tuesday, March 7, 2023 8:12AM - 8:24AM |
F07.00002: Exceptional order-by-disorder phenomena in non-reciprocally frustrated systems Cheyne Weis, Ryo Hanai Recently, a surprising analogy was given between geometric frustration and non-reciprocal interactions. Systems with antisymmetric couplings will generically contain a set of marginal orbits, which can be regarded as a dynamical counterpart of an accidental ground state degeneracy [1]. Imperfections were shown to lift the “accidental degeneracy” analogous to the so-called order-by-disorder phenomenon known to occur in geometrically frustrated systems. |
Tuesday, March 7, 2023 8:24AM - 8:36AM |
F07.00003: Spontaneous excitation of limit cycles in living chiral crystals Shreyas Gokhale, Yu-Chen Chao, Lisa Lin, Junang Li, Nikta Fakhri Broken parity and time reversal symmetries lead to the emergence of nonreciprocal interactions in chiral active matter. In a recent study, we observed a remarkable consequence of such emergent nonreciprocity in the form of spontaneous long-lived strain oscillations in living chiral crystals (LCCs) of starfish embryos (Tan*, Mietke* et al., Nature, 607, 287-293, 2022). Here, we combine insights from new experiments and data analyses to show that these long-lived oscillations correspond to limit cycles in strain space. The spontaneous excitation and eventual decay of strain oscillations results from the system switching stochastically between two attractors: a stable limit cycle, and a stable fixed point corresponding to the static ground state of the LCC. Our experimental observations are well-captured qualitatively by a minimal phenomenological nonlinear model comprising of nonreciprocal couplings between two strain fields and a global order parameter. The bistability between static and oscillatory states implies that oscillations can be induced using external perturbations in a controlled manner. Our results show that LCCs serve as paradigmatic active metamaterials in which nonreciprocity and nonlinearity combine to facilitate selective actuation of work generating limit cycles. |
Tuesday, March 7, 2023 8:36AM - 8:48AM |
F07.00004: Selective excitation of work-generating limit cycles in living chiral crystals Yu-Chen Chao, Shreyas Gokhale, Lisa Lin, Junang Li, Gary Choi, Nikta Fakhri Nonreciprocity is a ubiquitous feature of nonequilibrium systems, and often gives rise to novel forms of order, phase transitions and excitations in active matter. In living chiral crystals (LCCs) formed by spinning starfish embryos, nonreciprocity results in the spontaneous excitation of sustained strain waves that correspond to limit cycle oscillations. Here, we show that these limit cycles can be excited in a controlled manner by applying external mechanical perturbations in the form of uniaxial step compression. By applying a step compression protocol over a wide range of compression rates, we show that excitation of limit cycles is highly selective, and is triggered only when the applied compression rate is comparable to the embryo rotation frequency. This resonant coupling between imposed and intrinsic timescales provides a mechanism for selective work extraction from LCC strain oscillations. By quantifying time reversal asymmetry as well as the odd mechanical properties of the LCC, we calculate the work generation capacity of limit cycles. Our results have potential implications for engineering living metamaterials. |
Tuesday, March 7, 2023 8:48AM - 9:00AM |
F07.00005: Time-modulated chiral matter Ephraim S Bililign, Yehuda A Ganan, Alexis Poncet, Jessica E Metzger, Denis Bartolo, William T. M. Irvine In passive matter, structure and shape are dictated by effective interactions that are a function of the separation and orientation of the material's building blocks. Driving materials out of equilibrium allows these interactions to depend on time. We drive a collection of colloidal magnets to rotate with an angular speed that slows the rotation of the constituents at specific moments in time. The resulting interplay between spatial and temporal order provides effective control of internal structure, global morphology, and free surface stability. We interpret our observations in terms of the competition between time-modulated internal stresses and surface forces. |
Tuesday, March 7, 2023 9:00AM - 9:12AM |
F07.00006: Coarsening in odd elastic metamaterials Jack Binysh, Jonas Veenstra, Guido C Baardink, Anton Souslov, Corentin Coulais Non-reciprocal interactions in active elastic media cause work cycles and wave propagation forbidden in equilibrium. These linear phenomena yield motifs for programming robust mechanical actuation, but they also hint at a new class of non-linear emergent phenomena in active solids. |
Tuesday, March 7, 2023 9:12AM - 9:24AM |
F07.00007: Topological kinks in odd elastic metamaterials Jonas Veenstra Non-reciprocal interactions in mechanical materials can generate exciting material properties such as asymmetric (odd) elastic moduli. |
Tuesday, March 7, 2023 9:24AM - 9:36AM |
F07.00008: Hydrodynamic origins of odd viscosity in spinner monolayers Yehuda A Ganan, Ephraim S Bililign, Florencio Balboa Usabiaga, Alexis Poncet, Michael J Shelley, Denis Bartolo, William T Irvine Breaking parity and time-reversal in fluids allows to couple deformations to orthogonal stresses. This phenomenon translates into odd continuum material constants such as Hall viscosity. |
Tuesday, March 7, 2023 9:36AM - 9:48AM |
F07.00009: Confinement-induced phase transitions of Living Chiral Crystal Yuchao Chen, Nikta Fakhri Active crystal is a form of active matter with crystalline order, where the interplay between activity, elasticity and plasticity often leads to unusual dynamics. Self-assembled by swimming starfish embryos, the recently discovered Living Chiral Crystal (LCC) is an active crystal featuring non-reciprocal (chiral) interactions never found in a passive crystal. Here, we show how external boundary interaction and grain boundary/void connectivity induce different dynamics in LCC. Specifically, we confine LCC in regular polygons and circles, control void fraction, adjust grain boundary percolation, and observe phase transitions of LCC from local fluctuations to rigid body rotations and chaotic mixing. These results give another glimpse into how LCC acts as a model system to uncover new and rich properties of non-reciprocal active matter. |
Tuesday, March 7, 2023 9:48AM - 10:00AM |
F07.00010: Microscopic non-reciprocity drives emergent dynamic phase of living crystals Hyunseok Lee, Junang Li, Shreyas Gokhale, Lisa Lin, EliseAnne C Koskelo, Nikta Fakhri Active matter can exhibit non-equilibrium phases with emergent dynamics and work cycles. Theory suggests that non-reciprocal interactions in heterogeneous active matter can lead to novel time-dependent phases, but their relevance to living systems has not been demonstrated experimentally. Here we show that mixtures of swimming starfish embryos at different developmental stages spontaneously undergo transition from a dynamic phase to an ordered crystal. During the dynamic phase, the embryos exhibit chiral flocking in which the collective velocity rotates. The dynamics are persistent for hours, with repeated generation and disruption of the collective flocking.We further show that this oscillation in dynamic order is coupled with the oscillation in hexagonal order, hinting toward emergent non-reciprocal interaction between dynamics and structure. Finally, we demonstrate that the transition from dynamic to static phase is driven by the loss of microscopic non-reciprocity. |
Tuesday, March 7, 2023 10:00AM - 10:12AM |
F07.00011: High-resolution mapping of odd fluctuations and oscillations in living chiral crystals Lisa Lin, Jinghui Liu, Yuchao Chen, Yu-Chen Chao, Nikta Fakhri It has been shown that active crystals formed by self-assembling clusters of swimming starfish embryos exhibit signatures of odd mechanics, such as self-sustained chiral waves. How are these observed chiral waves and oscillations are actuated and how their dynamics couple to the formation and dissolution of the living chiral crystal? Here, we report the use of vibrational mode decomposition to dissect various non-equilibrium phases of the crystal dynamics. By analyzing embryo cluster trajectories over the time course of crystal formation and dissolution, we identify the spatial modes responsible for the collective actuation of an oscillatory active crystal both in spontaneous and mechanically excited conditions. We also report a direct extraction of dispersion relations from fluctuations of confined crystals to infer odd elastic moduli. Taken together, our results unveil the complex spatiotemporal origin of mechanical waves in non-reciprocal materials and provide insight on the design principles of collective phases of active metamaterials. |
Tuesday, March 7, 2023 10:12AM - 10:24AM |
F07.00012: The Mechanical Theory of Nonequilibrium Coexistence Ahmad K Omar Nonequilibrium phase transitions are routinely observed in both natural and synthetic systems. The ubiquity of these transitions highlights the conspicuous absence of a general theory of phase coexistence that is broadly applicable to both nonequilibrium and equilibrium systems. In this talk, we present a general mechanical theory for phase separation rooted in ideas explored nearly a half-century ago in the study of inhomogeneous fluids. The core idea is that the mechanical forces within the interface separating two coexisting phases uniquely determine coexistence criteria, regardless of whether a system is in equilibrium or not. We demonstrate the power and utility of this theory by applying it to active Brownian particles, predicting, from first principles, a quantitative phase diagram for motility-induced phase separation in both two and three dimensions. Finally, we extend and apply this mechanical perspective of phase coexistence to nonequilibrium order-disorder transitions and systems comprised of particles with nonreciprocal interactions. |
Tuesday, March 7, 2023 10:24AM - 10:36AM |
F07.00013: Signatures of odd dynamics in viscoelastic systems: from spatiotemporal pattern formation to odd rheology Carlos S Floyd, Aaron R Dinner, Suriyanarayanan Vaikuntanathan Non-reciprocal interactions fueled by local energy consumption are found in biological and synthetic active matter, where both viscosity and elasticity are often important. Such systems can be described by "odd" viscoelasticity, which assumes fewer material symmetries than traditional theories. In odd viscoelastic systems there is an interplay between the energy-consuming odd elastic elements and the traditional stabilizing elements. This leads to rich dynamical behavior which, due to a lack of appropriate numerical methods, has remained relatively unexplored. Furthermore, the implications associated with the presence of such odd terms in actomyosin and other similar anisotropic systems has not been addressed. Here, we study odd viscoelasticity analytically and using hydrodynamic simulations based on the lattice Boltzmann algorithm. We first outline how odd effects may naturally emerge from a theory of polymeric elasticity which can describe anisotropic systems like actomyosin. Next, we report on two striking features of odd viscoelastic dynamics: a pattern-forming instability which produces an oscillating array of fluid vortices, and strong transverse and rotational forces during a simulated rheological experiment. These findings can guide efforts to detect or engineer odd dynamics in soft active matter systems. |
Tuesday, March 7, 2023 10:36AM - 10:48AM |
F07.00014: Scaling of Moduli of Active and Thermal Elastic Membranes Mohamed El Hedi Bahri, Andrej Kosmrlj, Siddhartha Sarkar, Daniel Matoz Fernandez Non-equilibrium and active effects in mesoscopic scale systems are of great interest for study and applications. We will discuss the role of these non-equilibrium active effects in the context of thermally fluctuating 2-D elastic membranes. We implement a generalization of the elastic tensor that includes odd elastic moduli that break both conservation of energy and angular momentum, due to Colin Scheibner et al. Breaking these symmetries means that deformations from a reference state can induce chiral forces that cannot be derived from a Hamiltonian. Thus, the behavior of odd elastic membranes must instead be investigated via non-equilibrium Langevin equations. These mechanical properties are obtained via calculation of the correlation functions of local displacements. Indeed, Nelson and Frey calculated these correlation functions for energy-conserving and fully permeable elastic membranes and showed that one can recoup the universal positive and negative power-law exponents of the bending rigidity and shear modulus respectively (eta, eta_u) (these results were obtained originally by Nelson and Peliti using a Boltzmann weight). Ultimately, we are interested in observing whether the introduction of odd moduli will change the scaling behavior of classical elastic membranes. When introducing the odd elastic modulus K (which couples pure shear and simple shear), we show that it reduces with exponent 2*eta_u, thus leaving the Aronovitz-Lubensky fixed point stable. When introducing the odd elastic modulus A (which couples dilation strains and torques), we find the behavior to be less trivial. |
Tuesday, March 7, 2023 10:48AM - 11:00AM |
F07.00015: Dynamical scaling at critical exceptional points Shuoguang Liu, Ryo Hanai, Peter Littlewood In the many-body context, exceptional points (EPs), spectral singularities where eigenmodes completely coalesce, can possess similar properties to critical points due to the occurrence of gap closure [1,2]. This provides a new class of nonequilibrium phase transitions in generic nonequilibrium systems with spontaneously broken continuous symmetry characterized by coupled multiple-order parameters [2]. Surprisingly, at the critical exceptional point (CEP), it was shown that the critical fluctuations become anomalous giant (which diverges at d≤4) compared to the conventional case (which diverges at d≤2) [1]. However, it was found difficult to investigate the dynamical scaling in realistic spatial dimensions with standard analytical techniques, due to the anomalously enhanced many-body interaction effects. In our work, we perform a direct numerical study of driven many-body systems that exhibit CEPs. We found strong evidence of anomalous large long-time fluctuations as well as novel transient behaviors near the CEP. |
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