Microscopic molecular superfluid response: theory and simulations

TL;DR

This review discusses the theoretical and simulation studies of superfluidity in microscopic pH2 clusters, highlighting historical developments, key experimental findings, and future research directions in understanding quantum superfluid phenomena at nanoscale.

Contribution

It provides a comprehensive overview of the theoretical formalism and simulation results on pH2 superfluid clusters, serving as a guide for new researchers in the field.

Findings

Theoretical simulations support superfluidity in pH2 clusters.

Experimental evidence of pH2 superfluidity has been indirectly observed.

The review highlights future prospects for research in microscopic superfluid systems.

Abstract

Since its discovery in 1938, superfluidity has been the subject of much investigation because it provides a unique example of a macroscopic manifestation of quantum mechanics. About 60 years later, scientists successfully observed this phenomenon in the microscopic world though the spectroscopic Andronikashvili experiment in helium nano-droplets. This reduction of scale suggests that not only helium but also para-H2 (pH2) can be a candidate for superfluidity. This expectation is based on the fact that the smaller number of neighbours and surface effects of a finite-size cluster may hinder solidification and promote a liquid-like phase. The first prediction of superfluidity in pH2 clusters was reported in 1991 based on quantum Monte Carlo simulations. The possible superfluidity of pH2 was later indirectly observed in a spectroscopic Andronikashvili experiment in 2000. Since then, a growing number of studies have appeared, and theoretical simulations have been playing a special role because they help guide and interpret experiments. In this review, we go over the theoretical studies of pH2 superfluid clusters since the experiment of 2000. We provide a historical perspective and introduce the basic theoretical formalism along with key experimental advances. We then present illustrative results of the theoretical studies and comment on the possible future developments in the field. We include sufficient theoretical details such that the review can serve as a guide for newcomers to the field.