Critical fluctuations and anomalous transport in soft Yukawa-Langevin systems

TL;DR

This study uses Langevin-dynamics simulations to explore critical fluctuations and anomalous transport phenomena in soft dusty plasma systems, revealing non-Gaussian displacement distributions and intermittency without requiring non-equilibrium physics.

Contribution

The paper demonstrates that critical fluctuations and anomalous grain transport can emerge from a simple Langevin model without non-equilibrium physics, aligning with experimental observations.

Findings

Leptokurtic displacement distributions at short time scales

Development of humps in displacement distributions at multiples of inter-grain distance

Transition from bursty to vortical transport indicating intermittency

Abstract

Simulation of a Langevin-dynamics model demonstrates emergence of critical fluctuations and anomalous grain transport which have been observed in experiments on "soft" quasi-two-dimensional dusty plasma clusters. It has been suggested that these anomalies derive from particular non-equilibrium physics, but our model does not contain such physics: the grains are confined by an external potential, interact via static Yukawa forces, and are subject to stochastic heating and dissipation from neutrals. One remarkable feature is emergence of leptokurtic probability distributions of grain displacements $\xi(\tau)$ on time-scales $\tau<\tau_{\Delta}$, where $\tau_{\Delta}$ is the time at which the standard deviation $\sigma(\tau)\equiv < \xi^2(\tau) >^{1/2}$ approaches the mean inter-grain distance $\Delta$. Others are development of humps in the distributions on multiples of $\Delta$, anomalous Hurst exponents, and transitions from leptokurtic towards Gaussian displacement distributions on time scales $\tau>\tau_{\Delta}$. The latter is a signature of intermittency, here interpreted as a transition from bursty transport associated with hopping on intermediate time scales to vortical flows on longer time scales.