Muonium hydride: the lowest density crystal

TL;DR

This paper explores the unique properties of muonium hydride, revealing it forms the lowest density crystal known, with high melting temperature and enhanced superfluid response in nanoscale clusters, through first-principles quantum simulations.

Contribution

It presents the first detailed quantum simulation study of muonium hydride's phase diagram and properties, highlighting its extraordinarily low-density crystal phase and superfluid behavior.

Findings

Lowest density crystal known, lower than any other atomic or molecular crystal.

High melting temperature close to 9 K despite low density.

Enhanced superfluid response in nanoscale clusters.

Abstract

A muonium hydride molecule is a bound state of muonium and hydrogen atoms. It has half the mass of a parahydrogen molecule and very similar electronic properties in its ground state. The phase diagram of an assembly of such particles is investigated by first principle quantum simulations. In the bulk limit, the low-temperature equilibrium phase is a crystal of extraordinarily low density, lower than that of any other known atomic or molecular crystal. Despite the low density and particle mass, the melting temperature is surprisingly high (close to 9 K). No (metastable) supersolid phase is observed. We investigated the physical properties of nanoscale clusters (up to 200 particles) of muonium hydride and found the superfluid response to be greatly enhanced compared to that of parahydrogen clusters. The possible experimental realization of these systems is discussed.