Identification of time scales of the violation of the Stokes-Einstein relation in Yukawa liquids

Abstract

We investigate the origin of the violation of the Stokes-Einstein (SE) relation in two-dimensional Yukawa liquids. Using comprehensive molecular dynamics simulations, we identify the time scales supporting the violation of the SE relation $D\propto (\eta /T{)}^{-1}$, where $D$ is the self-diffusion coefficient and $\eta$ is the shear viscosity. We first compute the self-intermediate scattering function $F_s(k,t)$, the non-Gaussian parameter ${\alpha }_2$, and the autocorrelation function of the shear stress $C_{\eta }(t)$. The timescales obtained from these functions are included the structural relaxation time ${\tau }_{\alpha }$, the peak time of the non-Gaussian parameter ${\tau }_{{\alpha }_2}$, and the shear stress relaxation time ${\tau }_{\eta }$. We find that ${\tau }_{\eta }$ is coupled with $D$ for all temperatures indicating the SE preservation, however, ${\tau }_{\alpha }$ and ${\tau }_{{\alpha }_2}$ are decoupled with $D$ at low temperatures indicating the SE violation. Surprisingly, we find that the origins of this violation are related to the non-exponential behavior of the autocorrelation function of the shear stress and non-Gaussian behavior of the distribution function of particle displacements. These results confirm dynamic heterogeneity that occurs in two-dimensional Yukawa liquids that reflects the presence of regions in which dust particles move faster than the rest when the liquid cools to below the phase transition temperature.

References in corpus (4)

• Fractional Stokes-Einstein and Debye-Stokes-Einstein relations in a network forming liquid
• Dimensional Study of the Caging Order Parameter at the Glass Transition
• Self-diffusion in two-dimensional quasi-magnetized rotating dusty plasmas
• Fickian yet non-Gaussian diffusion in two-dimensional Yukawa liquids