Is the glassy dynamics same in 2D as in 3D? The Adam Gibbs relation test

Abstract

It has been recognized of late that even amorphous, glass-forming materials in two dimensions (2D) are significantly affected by Mermin-Wagner type long wavelength thermal fluctuation which is inconsequential in three (3D) and higher dimensions. Thus any study of glassy dynamics in 2D should first remove the effect of such fluctuations. The present work considers the question of whether the role of spatial dimension on glassy dynamics is only limited to such fluctuations, or whether the nature of glassy dynamics is intrinsically different in 2D. We address this issue by studying the relationship between dynamics and thermodynamics within the framework of the Adam-Gibbs (AG) relation and its generalization the Random First Order Transition (RFOT) theory. Using two model glass-forming liquids we find that even after removing the effect of long wavelength fluctuations, the AG relation breaks down in two dimensions. Then we consider the effect of anharmonicity of vibrational entropy - a second factor highlighted recently that can qualitatively change the nature of dynamics. We explicitly compute the configurational entropy both with and without the anharmonic correction. We show that the anharmonic correction reduces the extent of deviation from the AG relation, but even after taking into account its effects, the AG relation still breaks down in 2D. It is also more prominent if one considers diffusion coefficient rather than $\alpha$-relaxation time. Overall, the impact of the anharmonicity of vibration is larger than the long wavelength fluctuation in determining the qualitative relation between timescales and entropy. The extent and nature of deviation from the AG relation crucially depends on the attractive vs. repulsive nature of the inter-particle interaction. Thus our results suggest that the glassy dynamics in 2D may be intrinsically different from that in 3D.