Assessing the role of static lengthscales behind glassy dynamics in polydisperse hard disks

TL;DR

This study investigates the static correlation length in polydisperse hard disks and finds it decouples from the order associated with slow dynamics, challenging the universality of the point-to-set length as an indicator of glassy slowdown.

Contribution

The paper demonstrates that in polydisperse hard disks, the point-to-set length does not correlate with the growth of hexatic order, questioning its role in glassy dynamics.

Findings

PTS length mirrors two-body density decay length

Decoupling of PTS length from hexatic order growth

Challenges the order-agnostic assumption of PTS length

Abstract

The possible role of growing static order in the dynamical slowing down towards the glass transition has recently attracted considerable attention. On the basis of random first-order transition (RFOT) theory, a new method to measure the static correlation length of amorphous order, called "point-to-set (PTS)" length, has been proposed, and used to show that the dynamic length grows much faster than the static length. Here we study the nature of the PTS length, using a polydisperse hard disk system, which is a model that is known to exhibit a growing hexatic order upon densification. We show that the PTS correlation length is decoupled from the steeper increase of the correlation length of hexatic order, while closely mirroring the decay length of two-body density correlations. Our results thus provide a clear example that other forms of order can play an important role in the slowing down of the dynamics, casting a serious doubt on the order agnostic nature of the PTS length and its relevance to slow dynamics, provided that a polydisperse hard disk system is a typical glass former.