Revealing the supercritical dynamics of dusty plasmas and their liquid-like to gas-like dynamical crossover

TL;DR

This study uses molecular dynamics simulations to demonstrate that dusty plasmas exhibit supercritical fluid behavior with a liquid-like to gas-like dynamical crossover, revealing universal features and new diagnostics for this transition.

Contribution

It introduces multiple diagnostics to locate the Frenkel line in dusty plasmas and proposes a new criterion based on the ratio of transverse sound speed to particle speed.

Findings

Dusty plasmas display supercritical fluid characteristics.

The Frenkel line can be identified using various diagnostics.

The dynamical transition temperature is always 20 times the melting point.

Abstract

Dusty plasmas represent a powerful playground to study the collective dynamics of strongly coupled systems with important interdisciplinary connections to condensed matter physics. Due to the pure Yukawa repulsive interaction between dust particles, dusty plasmas do not display a traditional liquid-vapor phase transition, perfectly matching the definition of a supercritical fluid. Using molecular dynamics simulations, we verify the supercritical nature of dusty plasmas and reveal the existence of a dynamical liquid-like to gas-like crossover which perfectly matches the salient features of the Frenkel line in classical supercritical fluids. We present several diagnostics to locate this dynamical crossover spanning from local atomic connectivity, shear relaxation dynamics, velocity autocorrelation function, heat capacity, and various transport properties. All these different criteria well agree with each other and are able to successfully locate the Frenkel line in both 2D and 3D dusty plasmas. In addition, we propose the unity ratio of the instantaneous transverse sound speed $C_T$ to the average particle speed $\bar{v}_{p}$, i.e., $C_T / \bar{v}_{p} = 1$, as a new diagnostic to identify this dynamical crossover. Finally, we observe an emergent degree of universality in the collective dynamics and transport properties of dusty plasmas as a function of the screening parameter and dimensionality of the system. Intriguingly, the temperature of the dynamical transition is independent of the dimensionality, and it is found to be always $20$ times of the corresponding melting point. Our results open a new path for the study of single particle and collective dynamics in plasmas and their interrelation with supercritical fluids in general.