# Direct Observation of Entropic Stabilization of bcc Crystals Near Melting

## TL;DR

This study demonstrates how entropic effects stabilize bcc colloidal crystals near melting, with large fluctuations and nonaffine displacements causing a breakdown of classical lattice dynamics.

## Contribution

It provides experimental evidence of entropic stabilization and introduces a reformulated theory accounting for nonaffinity in crystal melting.

## Key findings

- Large fluctuations stabilize bcc colloidal crystals.
- Nonaffine displacements vanish shear modulus at melting.
- Classical lattice dynamics fail near transition.

## Abstract

Crystals with low latent heat are predicted to melt from an entropically stabilized body-centered cubic symmetry. At this weakly first-order transition, strongly correlated fluctuations are expected to emerge, which could change the nature of the transition. Here we show how large fluctuations stabilize bcc crystals formed from charged colloids, giving rise to strongly power-law correlated heterogeneous dynamics. Moreover, we find that significant nonaffine particle displacements lead to a vanishing of the nonaffine shear modulus at the transition. We interpret these observations by reformulating the Born-Huang theory to account for nonaffinity, illustrating a scenario of ordered solids reaching a state where classical lattice dynamics fail.