Absence of superfluidity in a quasi one-dimensional parahydrogen fluid adsorbed inside carbon nanotubes

TL;DR

First principle simulations demonstrate that parahydrogen inside carbon nanotubes forms a crystalline, non-superfluid phase, contradicting previous claims of superfluidity based on flawed effective interaction models.

Contribution

This study provides conclusive numerical evidence that parahydrogen in nanotubes is non-superfluid and clarifies the inaccuracies of prior effective potential approaches.

Findings

Parahydrogen forms a crystalline shell on the nanotube surface.

The central column of parahydrogen shows no superfluid behaviour.

Previous superfluid predictions were based on incorrect interaction models.

Abstract

A recent claim of superfluid behaviour of parahydrogen adsorbed inside armchair carbon nanotubes [M. Rossi and F. Ancilotto, Phys. Rev. B 94, 100502 (2016)] is disproven by means of first principle computer simulations. Conclusive numerical evidence shows that the low temperature equilibrium thermodynamic phase of parahydrogen adsorbed inside a (10,10) armchair nanotube features a crystalline shell adsorbed on the inner surface of the tube, and a well separated quasi one-dimensional central column showing no evidence of possible fluid or superfluid behaviour. Rather, the system is quasi-crystalline and non-superfluid; its physical character is qualitatively identical to that observed in similar confined settings extensively studied in the past. The incorrect prediction of superfluidity stems from the erroneous use of an effective one-dimensional interaction potential that does not describe parahydrogen at the center of the nanotube.