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Structure, superfluidity, and quantum melting of hydrogen clusters

Fabio Mezzacapo·Massimo Boninsegni
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Abstract

We present results of a theoretical study of para-hydrogen and ortho-deuterium clusters at low temperature (0.5 K < T < 3.5 K), based on Path Integral Monte Carlo simulations. Clusters of size up to N=21 para-hydrogen molecules are nearly entirely superfluid at T < 1 K. For 21 < N < 30, the superfluid response displays strong variations with N, reflecting structural changes that occur on adding or removing even a single molecule. Some clusters in this size range display quantum melting, going from solid- to liquid-like as T tends to 0. Melting is caused by quantum exchanges of molecules. The largest para-hydrogen cluster for which a significant superfluid response is observed comprises 27 molecules. Evidence of a finite superfluid response is presented for ortho-deuterium clusters of size up to 14 molecules. Magic numbers are observed, at which both types of clusters feature pronounced stability.

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Fabio Mezzacapo, Massimo Boninsegni. 2007-03-14. Structure, superfluidity, and quantum melting of hydrogen clusters. https://doi.org/10.1103/physreva.75.033201

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