Plati A, Baldassarri A, Gnoli A, Gradenigo G, Puglisi A
Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy.
Istituto dei Sistemi Complessi-CNR and Dipartimento di Fisica, Università di Roma Sapienza, P.le Aldo Moro 2, 00185, Rome, Italy.
Phys Rev Lett. 2019 Jul 19;123(3):038002. doi: 10.1103/PhysRevLett.123.038002.
Recent experiments with rotational diffusion of a probe in a vibrated granular media revealed a rich scenario, ranging from a dilute gas to a dense liquid with cage effects and an unexpected superdiffusive behavior at large times. Here we set up a simulation that reproduces quantitatively the experimental observations and allows us to investigate the properties of the host granular medium, a task not feasible in the experiment. We discover a persistent collective rotational mode which emerges at a high density and a low granular temperature: a macroscopic fraction of the medium slowly rotates, randomly switching direction after very long times. Such a rotational mode of the host medium is the origin of the probe's superdiffusion. Collective motion is accompanied by a kind of dynamical heterogeneity at intermediate times (in the cage stage) followed by a strong reduction of fluctuations at late times, when superdiffusion sets in.
最近在振动颗粒介质中对探针旋转扩散进行的实验揭示了一种丰富的情形，范围从稀薄气体到具有笼效应的稠密液体，以及在长时间时出现的意外超扩散行为。在这里，我们建立了一个模拟，该模拟定量地再现了实验观测结果，并使我们能够研究主体颗粒介质的性质，这是实验中无法完成的任务。我们发现了一种持续的集体旋转模式，它出现在高密度和低颗粒温度下：介质的宏观部分缓慢旋转，在很长时间后随机改变方向。主体介质的这种旋转模式是探针超扩散的起源。集体运动在中间时间（在笼阶段）伴随着一种动力学不均匀性，随后在超扩散开始的后期波动强烈减小。
