Vortex arrays in nanoscopic superfluid helium droplets

TL;DR

This study investigates vortex array formation in rotating superfluid helium-4 nanodroplets at zero temperature using density functional theory, comparing results with classical models and recent experimental observations.

Contribution

It provides a quantum mechanical analysis of vortex arrays in nanodroplets, confirming experimental shapes and stability beyond classical predictions.

Findings

Droplet shape transitions from pseudo-spheroid to wheel-like with increasing vortices.

Droplets remain stable above classical stability limits.

Vortex arrays are consistent with experimental observations.

Abstract

We have studied the appearance of vortex arrays in a rotating helium-4 nanodroplet at zero temperature within density functional theory. Our results are compared with those for classical rotating fluid drops used to analyze the shape and vorticity in recent experiments [L.F. Gomez et al., Science 345, 906 (2014)], where vortices have been directly seen in superfluid droplets for the first time. In agreement with the experiments, we have found that the shape of the droplet changes from pseudo-spheroid, oblate-like for a small number of vortices to a peculiar "wheel-like" shape, delimited by nearly flat upper and lower surfaces, when the number of vortices is large. Also in agreement with the experiments, we have found that the droplet remains stable well above the stability limit predicted by classical theories.