The Dilemma of Bose Solids: is He Supersolid?

TL;DR

This paper discusses the controversy over whether solid helium-4 exhibits supersolidity, highlighting experimental ambiguities, theoretical support, and the need for clearer understanding of the ground state wave-function.

Contribution

It reviews the experimental and theoretical debates on supersolidity in helium-4 and emphasizes the importance of clarifying the ground state wave-function for resolution.

Findings

Experimental evidence is conflicting and some claims have been retracted.

Theoretical models support the possibility of supersolidity in Bose-Hubbard systems.

Accurate simulations are limited by assumptions about phase coherence.

Abstract

Nearly a decade ago the old controversy about possible superfluid flow in the ground state of solid He4 was revived by the apparent experimental observation of such superflow. Although the experimentalists have recently retracted, very publicly, some of the observations on which such a claim was based, other confirming observations of which there is no reason for doubt remain on the record. Meanwhile theoretical arguments bolstered by some experimental evidence strongly favor the existence of supersolidity in the Bose-Hubbard model, and these arguments would seem to extend to solid He. The true situation thus is apparently extraordinarily opaque. The situation is complicated by the fact that all accurate simulation studies on Heuse the uniform sign hypothesis which confines them to the phase-coherent state, which is, in principle, supersolid, so that no accurate simulations of the true, classical solid exist. There is great confusion as to the nature of the ground state wave-function for a bose quantum solid, and we suggest that until that question is cleared up none of these dilemmas will be resolved.