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.
Highlights
An intriguing open question in condensed matter physics, one with potential practical significance, is whether there exists a lower bound for the density of a crystal
The low-temperature phase diagram of the thermodynamic system described by Eq (1) as a function of density and temperature has been studied in this work by means of firstprinciples numerical simulations, based on the continuousspace worm algorithm [21,22]
We have investigated the low-temperature phase diagram of a bulk assembly of muonium hydride molecules, by means of first-principles quantum simulations
Summary
An intriguing open question in condensed matter physics, one with potential practical significance, is whether there exists a lower bound for the density of a crystal. Crystallization occurs at low temperatures (T ) in almost all known substances, as the state of lowest energy (ground state) is approached. The ground state is one in which the potential energy of the interaction among the constituent particles is minimized, a condition that corresponds to an orderly arrangement of particles in regular, periodic lattices. Quantum mechanics affects this fundamental conclusion only quantitatively, as the zero-point motion of particles results in lower equilibrium densities and melting temperatures, with respect to what one would predict classically; typically, these corrections are relatively small.
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