Quasi-2D parahydrogen: On the verge of turning superfluid?

TL;DR

First principle simulations of thin parahydrogen films on silica at low temperatures show no evidence of superfluidity, indicating the top layer remains an insulating crystal rather than a superfluid, contrary to some experimental claims.

Contribution

This study provides first-principles computational evidence that contradicts recent experimental claims of superfluidity in quasi-2D parahydrogen films.

Findings

Top layer remains an insulating crystal

No quantum exchanges observed in the top layer

Simulation results match experimental densities

Abstract

First principle computer simulations of a thin parahydrogen film adsorbed on a silica substrate at low temperature (below 6 K) yield no evidence that the top layer is liquid and/or in the proximity of a superfluid transition, as claimed in recent experimental work [T. Makiuchi et al., Phys. Rev. Lett. 123, 245301 (2019)]. Computed values of first and second layer completion densities are in quantitative agreement with experiment, but as observed also on other substrates, the top layer is an insulating crystal, quantum-mechanical exchanges of molecules are non-existent, and the overall physical behavior of the system can be understood largely along classical lines.