Vortices in quantum droplets of heteronuclear Bose mixtures

TL;DR

This paper theoretically investigates vortex structures in self-bound heteronuclear Bose mixtures, revealing favored vortex formation, core development, and angular momentum behavior, with similarities to superfluid helium droplets.

Contribution

It provides a detailed theoretical analysis of vortex formation and angular momentum in heteronuclear quantum droplets, including beyond-mean-field effects and comparison to classical rotating droplets.

Findings

Linear vortices are energetically favored in the heavier species.

A fake core develops in the other species, creating a detectable hole.

Vortex presence leads to a two-branch stability diagram similar to classical droplets.

Abstract

We have theoretically investigated the structure of spinning self-bound droplets made of $^{41}$K-$^{87}$Rb Bose mixture by solving the Gross-Pitaevskii equation including beyond-mean-field correction in the Lee-Huang-Yang form. The structure and energetics of vortex formation in the self-bound mixture have been elucidated, showing that the formation of linear vortices in the heavier species is energetically favoured over other configurations. A fake (partially filled) core develops as a consequence in the other species, resulting in a hole which might be imaged in experiments. The interplay between vortices and capillary waves, which are the two ways angular momentum can be stored in a swirling superfluid, is studied in detail by computing the relation between angular momentum and rotational frequency. The results show intriguing similarities with the case of a prototypical superfluid, i.e. $^4$He droplets when set into rotation. A two-branches curve in the stability diagram, qualitatively similar to the one expected for classical (incompressible and viscous) rotating liquid droplets, is obtained when vortices are present in the droplets, while prolate (i.e. non axi-symmetric) shapes are only permitted in vortex-free droplets.