Regensburg 2022 – wissenschaftliches Programm
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BP: Fachverband Biologische Physik
BP 11: Active Matter 2 (joint session DY/BP/CPP)
BP 11.3: Vortrag
Dienstag, 6. September 2022, 10:30–10:45, H18
Long-Range Nematic Order in Two-Dimensional Active Matter — •Benoît Mahault1 and Hugues Chaté2,3 — 1MPIDS, 37077 Göttingen, Germany — 2SPEC, CEA-Saclay, 91191 Gif-sur-Yvette, France — 3CSRC, Beijing 100193, China
Studies of active matter continue to flourish, exploring more and more complex situations in an increasingly quantitative manner. Evidence has accumulated that shows active matter exhibits properties that are impossible in thermal equilibrium or even in driven systems. In spite of all this progress, important fundamental questions remain open. Such a long-standing issue is whether true long-range nematic order can emerge in two space dimensions. In this talk, we will present theoretical and numerical results obtained from minimal models of self-propelled polar particles aligning nematically. Our study shows that the orientational order emerging from such systems is quasi-long-ranged beyond the scale associated to induced velocity reversals, which is typically extremely large and often cannot even be measured. On scales where particle motion is ballistic, nematic order appears truly long-range. A hydrodynamic theory for this de facto phase is derived, and we show that its structure and symmetries differ from conventional descriptions of both polar flocks and active nematics. Our analysis of this field theory predicts π-symmetric propagative sound modes and the scaling form of space-time fluctuations. Finally, numerical results confirm the theory and allow us to estimate all scaling exponents.