Can liquid metal surfaces have hexatic order?

TL;DR

This study suggests that supercooled heavy noble liquid metals, like gold, can develop surface hexatic order due to orientational correlations, with a transition occurring below melting but being preempted by recrystallization.

Contribution

It introduces the possibility of hexatic order at liquid metal surfaces and provides simulation evidence for a surface hexatic transition in supercooled gold.

Findings

Surface layers of liquid Au resemble defected 2D triangular solids.

Supercooling decreases disclination density as predicted by theory.

A surface hexatic transition occurs around 350 K below melting.

Abstract

We propose that extended orientational correlations can appear at the surface of supercooled heavy noble liquid metals, due to the same compressive forces that cause reconstruction of their crystal surfaces. Simulations for liquid Au show a packed surface layer structurally akin to a defected 2D triangular solid. Upon supercooling, the density of unbound disclinations decreases as expected in Nelson-Halperin's theory. It extrapolates to a hexatic transition about 350 K below melting, where a sharp growth of orientational correlation length and time is also found. True hexatic order is preempted by surface-initiated recrystallisation.