Quasi-2D H2: On the Verge of Turning Superfluid?

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 (Makiuchi et al. in 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.

Automated summary

First-principle computer simulations show no evidence of a liquid top layer or proximity to a superfluid transition in a thin parahydrogen film adsorbed on a silica substrate at low temperatures, contradicting recent experimental claims. The top layer is found to be an insulating crystal without quantum-mechanical exchanges between molecules, consistent with observations on other substrates.