Dynamics in two-dimensional glassy systems of crowded Penrose kites

TL;DR

This study explores the complex relaxation dynamics of a two-dimensional system of Penrose kites, revealing decoupling between diffusion and relaxation times, and different dynamical processes for translation and rotation in glassy states.

Contribution

It provides new insights into the decoupling of translational and rotational dynamics and the nature of dynamical heterogeneities in 2D glassy Penrose kite systems.

Findings

Decoupling between diffusion coefficients and relaxation times in both regimes.

Dynamical heterogeneities are spatial for translation and temporal for rotation.

Different dynamical length scales govern translational and rotational motions.

Abstract

We investigate the translational and rotational relaxation dynamics of a crowded two-dimensional system of monodisperse Penrose kites, in which crystallization, quasi-crystallization, and nematic ordering are suppressed, from low to high area fractions along the metastable ergodic fluid branch. First, we demonstrate a decoupling between both the translational and the rotational diffusion coefficients and the relaxation time: the diffusivities are not inversely proportional to the relaxation time, neither in the low-density normal liquid regime nor in the high-density supercooled regime. Our simulations reveal that this inverse proportionality breaks in the normal liquid regime due to the Mermin-Wagner long-wavelength fluctuations and in the supercooled regime due to the dynamical heterogeneities. We then show that dynamical heterogeneities are mainly spatial for translational degrees of freedom and temporal for rotational ones, that there is no correlation between the particles with the largest translational and rotational displacements, and that different dynamical length scales characterize the translational and the rotational motion. Hence, despite the translational and the rotational glass-transition densities coincide, according to a mode-coupling fit, translations and rotations appear to decorrelate via different dynamical processes.