Supersolid and the non-uniform condensate

TL;DR

This paper proposes a model of a non-uniform condensate with a spatially modulated order parameter that exhibits both solid-like density waves and superfluid flow, potentially explaining experimental observations in solid helium-4.

Contribution

It introduces a semi-phenomenological model of a supersolid with a modulated order parameter and explores flow-induced phase transitions.

Findings

Identifies a non-classical translational inertia in the model.

Connects the model to experimental non-classical rotational inertia in helium-4.

Suggests a supersolid-to-superfluid transition induced by flow.

Abstract

We construct a model of non-uniform condensate having a spatially modulated complex order parameter that makes it kinematically an x-ray solid, i.e., a real mass density wave, but one admitting an associated superfluid flow. Intrinsic to this state is a non-classical translational inertia which we derive for the case of a potential flow. Connection to the non-classical rotational inertia observed in recent experiments on solid helium-4 is discussed. Our semi-phenomenological treatment suggests a flow-induced supersolid-to-superdfluid transition.