Laboratoire de Physique Statistique, Département de physique de l'ENS, Ecole Normale Supérieure, PSL Research University, Université Paris Diderot, Sorbonne Paris Cité, Sorbonne Universités, UPMC Univ. Paris 06, CNRS, 75005, Paris, France.
Max-Planck-Institut für Physik komplexer Systeme, Nöthnitzer Str. 38, 01187, Dresden, Germany.
Nat Commun. 2018 Nov 28;9(1):5045. doi: 10.1038/s41467-018-07491-5.
Active matter has been much studied for its intriguing properties such as collective motion, motility-induced phase separation and giant fluctuations. However, it has remained unclear how the states of active materials connect with the equilibrium phases. For two-dimensional systems, this is also because the understanding of the liquid, hexatic, and solid equilibrium phases and their phase transitions is recent. Here we show that two-dimensional self-propelled point particles with inverse-power-law repulsions moving with a kinetic Monte Carlo algorithm without alignment interactions preserve all equilibrium phases up to very large activities. Furthermore, at high activity within the liquid phase, a critical point opens up a gas-liquid motility-induced phase separation region. In our model, two-step melting and motility-induced phase separation are thus independent phenomena. We discuss the reasons for these findings to be common to a wide class of two-dimensional active systems.
活性物质因其有趣的特性而备受研究，例如集体运动、运动诱导的相分离和巨涨落。然而，活性物质的状态如何与平衡相联系，这一点仍不清楚。对于二维系统，这也是因为对液体、六方和固体平衡相及其相变的理解是最近的。在这里，我们表明，具有反幂律排斥力的二维自主点粒子在没有对齐相互作用的情况下，通过动力学蒙特卡罗算法移动，可以保持所有平衡相，直到非常大的活性。此外，在液相中的高活性下，临界点会打开一个气-液运动诱导的相分离区域。在我们的模型中，两步熔化和运动诱导的相分离是独立的现象。我们讨论了这些发现适用于广泛的二维活性系统的原因。
