Experimental evidence of the Frenkel line in supercritical neon

TL;DR

This study provides experimental evidence of a structural crossover in supercritical neon, supporting the existence of the Frenkel line and linking structural changes to dynamical and thermodynamic property shifts.

Contribution

First experimental verification of the Frenkel line in supercritical neon through structural analysis at high pressure and temperature conditions.

Findings

Observed change in medium-range order structure with pressure.

Detected crossover in short-range order via coordination number.

Crossover width less than 10-12% in pressure and temperature.

Abstract

Recent research suggests that the supercritical state consists of liquidlike and gaslike states where particle dynamics and key system properties are qualitatively different. We report experimental evidence of the structural crossover in supercritical neon at pressure and temperature conditions significantly exceeding the critical point values: 250$\,P_c$ and 6.6$\,T_c$. The experimental results show a crossover of the medium-range order structure evidenced by the change of the structure factor with pressure. We also observe the crossover of the short-range order structure indicated by changes in the coordination number. The relative width of the crossover is fairly narrow and is smaller than 10-12 \% in pressure and temperature. By comparing our experimental results with molecular dynamics simulations, we suggest that the observed crossover can be attributed to the Frenkel line and discuss the relationship between the structural crossover and qualitative changes of dynamical and thermodynamic properties of supercritical matter.