Superfluidity of isotopically doped parahydrogen clusters

TL;DR

Computer simulations reveal that replacing a few molecules in large para-hydrogen clusters with heavier isotopes like ortho-deuterium can suppress superfluidity and induce solid-like behavior, affecting their quantum properties.

Contribution

This study demonstrates how isotopic substitution influences superfluidity in hydrogen clusters, highlighting the significant impact of a small number of heavier isotopes.

Findings

Replacing 1-2 molecules with ortho-deuterium suppresses superfluidity.

Ortho-deuterium prefers the cluster's interior, while ortho-hydrogen stays near the surface.

Small isotope changes can induce solid-like behavior in large clusters.

Abstract

It is shown by computer simulations that superfluid {\it para}-hydrogen clusters of more than 22 molecules can be turned insulating and "solidlike" by the replacement of as few as one or two molecules, with ones of the heavier {\it ortho}-deuterium isotope. A much smaller effect is observed with substitutional {\it ortho}-hydrogen. Substitutional {\it ortho}-deuterium molecules prevalently sit in the inner part of the cluster, whereas {\it ortho}-hydrogen impurities reside primarily in the outer shell, near the surface. Implications on the superfluidity of pure {\it para}-hydrogen clusters are discussed.