Superfluid Interfaces in Quantum Solids

TL;DR

This paper explores the possibility of superfluid interfaces in quantum solids like helium-4, showing they can exist under various conditions and undergo quantum phase transitions, with implications for understanding non-classical inertia.

Contribution

It demonstrates that superfluidity at interfaces between solid domains can occur in simple quantum crystal models and characterizes the nature of the associated quantum phase transitions.

Findings

Superfluid interfaces can exist in a wide parameter range.

A quantum phase transition can turn a superfluid interface into an insulator.

In 2D, superfluidity onset is linked to interface roughening and topological excitations.

Abstract

One scenario for the non-classical moment of inertia of solid He-4 discovered by Kim and Chan [Nature 427, 225 (2004)] is the superfluidity of micro-crystallite interfaces. On the basis of the most simple model of a quantum crystal--the checkerboard lattice solid--we show that the superfluidity of interfaces between solid domains can exist in a wide range of parameters. At strong enough inter-particle interaction, a superfluid interface becomes an insulator via a quantum phase transition. Under the conditions of particle-hole symmetry, the transition is of the standard U(1) universality class in 3D, while in 2D the onset of superfluidity is accompanied by the interface roughening, driven by fractionally charged topological excitations.