Superglass Phase of Helium-four

TL;DR

This paper investigates the low-temperature phases of Helium-4 using advanced Monte Carlo simulations, revealing the emergence of a superglass phase characterized by amorphous structure and superfluidity.

Contribution

It introduces a novel simulation approach to study Helium-4 phases and demonstrates the existence of a superglass phase with unique properties.

Findings

Disordered Helium-4 can form a superglass with superfluidity.

Ideal crystal remains an insulator at low temperatures.

Initial conditions influence the resulting phase.

Abstract

We study different solid phases of Helium-four, by means of Path Integral Monte Carlo simulations based on a recently developed "worm" algorithm. Our study includes simulations that start off from a high-T gas phase, which is then "quenched" down to T=0.2 K. The low-T properties of the system crucially depend on the initial state. While an ideal hcp crystal is a clear-cut insulator, the disordered system freezes into a "superglass", i.e., a metastable amorphous solid featuring off-diagonal long-range order and superfluidity.