Phase diagram of muonium hydride: when dimensionality matters

TL;DR

This study explores how reducing dimensionality from three to two significantly alters the phase diagram of muonium hydride, revealing a superfluid phase in two dimensions absent in three-dimensional behavior.

Contribution

It provides the first detailed theoretical analysis showing drastic changes in phase behavior of muonium hydride due to dimensional reduction.

Findings

Two-dimensional muonium hydride exhibits a superfluid phase at ~2.2 K.

In 2D, it has a liquid phase similar to He-4, unlike the 3D case.

Dimensionality critically influences the phase diagram of this material.

Abstract

We carry out a theoretical investigation of the low-temperature phase diagram of muonium hydride in two dimensions, using numerical simulations. It is shown that the phase diagram of this substance is qualitatively different in two and three dimensions. Specifically, while in three dimensions it has been shown to be essentially identical to that of parahydrogen, i.e., only displaying a single (crystalline) phase, in two dimensions it is very similar to that of He-4, with an equilibrium liquid phase that turns superfluid at a temperature as high as ~ 2.2 K, and that crystallizes under applied pressure. To our knowledge, this is the first well-described case of a condensed matter system whose phase diagram is drastically altered by dimensional reduction.