Preliminary Heat Capacity and Vapor Pressure Measurements of 2D 4He on ZYX Graphite

TL;DR

This study presents preliminary heat capacity and vapor pressure data for 2D helium-4 on ZYX graphite, revealing clearer phase distinctions due to ZYX's superior crystallinity and identifying the second-layer promotion density.

Contribution

It provides new measurements on 2D helium-4 on ZYX graphite, highlighting differences from previous Grafoil-based studies and offering insights into phase behavior and layer promotion.

Findings

Asymmetric density dependence of heat-capacity peak for 1/3 phase

Second-layer promotion density determined as 11.8±0.3 nm^-2

Enhanced phase distinction due to ZYX's crystallinity

Abstract

We report preliminary heat capacity and vapor pressure measurements of the first and second layers of 4He adsorbed on ZYX graphite. ZYX is known to have much better crystallinity than Grafoil, the most commonly-used exfoliated graphite substrate, such as a ten-times larger platelet size. This allows us to distinguish different phases in 2D helium-4 much more clearly and may provide qualitatively different insights into this system. We found a significantly asymmetric density-dependence of the heat-capacity peak associated with the 1/3 phase formation comparing with that obtained with Grafoil. The 2nd-layer promotion density is determined as 11.8+-0.3 nm-2 from the heat-capacity measurement of low density samples in the 2nd layer and vapor pressure measurement.