Energetics and Possible Formation and Decay Mechanisms of Vortices in Helium Nanodroplets

TL;DR

This paper investigates the energy and angular momentum of vortex states in helium nanodroplets, exploring their formation mechanisms, stability, and potential decay pathways based on droplet size and collision processes.

Contribution

It provides a detailed analysis of vortex energetics and formation mechanisms in helium nanodroplets, highlighting conditions under which vortices are likely to form and remain stable.

Findings

Vortices can form during heavy solute pickup due to deposited energy and angular momentum.

Curved vortex lines can exist at very low energy and angular momentum levels.

Most vortices are predicted to be stable at 0.38 K despite high energy.

Abstract

The energy and angular momentum of both straight and curved vortex states of a helium nanodroplet are examined as a function of droplet size. For droplets in the size range of many experiments, it is found that during the pickup of heavy solutes, a significant fraction of events deposit sufficient energy and angular momentum to form a straight vortex line. Curved vortex lines exist down to nearly zero angular momentum and energy, and thus could in principle form in almost any collision. Further, the coalescence of smaller droplets during the cooling by expansion could also deposit sufficient angular momentum to form vortex lines. Despite their high energy, most vortices are predicted to be stable at the final temperature (0.38 K) of helium nanodroplets due to lack of decay channels that conserve both energy and angular momentum.