Layering and superfluidity of soft-core bosons in shallow spherical traps

TL;DR

This study uses Monte Carlo simulations to explore how soft-core bosons in spherical traps form shell structures with specific symmetries and exhibit non-uniform superfluidity, revealing complex phase behaviors in curved confinement.

Contribution

It demonstrates the formation of symmetric shell structures and superfluidity patterns in soft-core bosons under spherical confinement, highlighting novel geometric and phase transition phenomena.

Findings

Shell structures with icosahedral and dodecahedral symmetry form at specific parameters.

Superfluid density varies non-uniformly with radius and vanishes before cluster melting.

Classical and distinguishable particles show similar shell patterns but are more thermally fragile.

Abstract

Fundamental theories and models of many-body physics can be probed in experiments on ultracold atoms held in place by electromagnetic fields. In particular, of considerable interest are systems under curved confinement, since they can yield exotic states of matter which would be impossible to obtain in flat space. In this study we focus on relatively small samples, where curvature effects are stronger, and analyze by Monte Carlo simulations the peculiar structure arising in an assembly of soft-core bosons subject to a weak trapping potential with spherical symmetry. Upon suitable tuning of the parameters, a hundred particles or so group together in clusters arranged in a shell with icosahedral symmetry. As the number of particles increases, a second shell gradually develops, concentric to (and partly overlapping with) the original one, where clusters are in perfect registry with the first shell, thus forming a dodecahedral pattern. Cluster arrangements with the symmetry of other polyhedra are seen for different sets of parameters. At low temperature the superfluid density is non-uniform in the radial direction; heating the system progressively, superfluidity eventually vanishes while still clusters are present, a behavior resembling the transition from supersolid to normal solid on a plane. Two shells of clusters are also observed in systems of classical or distinguishable quantum particles, but in those cases the shells are more fragile to thermal fluctuations. All these behaviors can in principle be tested in systems of Rydberg-dressed atoms loaded into a bubble trap.