Sorbonne Université, CNRS, Laboratoire de Physique Théorique de la Matière Condensée, 75005 Paris, France.
Service de Physique de l'Etat Condensé, CEA, CNRS Université Paris-Saclay, CEA-Saclay, 91191 Gif-sur-Yvette, France.
Phys Rev Lett. 2022 May 20;128(20):208004. doi: 10.1103/PhysRevLett.128.208004.
We study the effect of spatial anisotropy on polar flocks by investigating active q-state clock models in two dimensions. In contrast to the equilibrium case, we find that any amount of anisotropy is asymptotically relevant, drastically altering the phenomenology from that of the rotationally invariant case. All of the well-known physics of the Vicsek model, from giant density fluctuations to microphase separation, is replaced by that of the active Ising model, with short-range correlations and complete phase separation. These changes appear beyond a length scale that diverges in the q→∞ limit, so that the Vicsek-model phenomenology is observed in finite systems for weak enough anisotropy, i.e., sufficiently high q. We provide a scaling argument which explains why anisotropy has such different effects in the passive and active cases.
我们通过研究二维中的活性 q 态钟模型来研究空间各向异性对极地群的影响。与平衡情况不同，我们发现任何数量的各向异性都是渐近相关的，这极大地改变了各向同性情况下的现象学。Vicsek 模型的所有著名物理学，从巨大的密度涨落到微相分离，都被活性伊辛模型所取代，具有短程相关性和完全相分离。这些变化出现在 q→∞极限发散的长度尺度之外，因此在足够弱的各向异性下，即足够高的 q，有限系统中可以观察到 Vicsek 模型的现象学。我们提供了一个标度论证，解释了为什么各向异性在被动和主动情况下会有如此不同的影响。
