Dynamics of impurity clustering in superfluid He-4 nanodroplets

The capture of multiple impurities by He-4 droplets is investigated using real time dynamics within the density functional approach applied to liquid helium. We study the case of two or six Ar atoms colliding with a He-4(5000) droplet either in its ground state or hosting a six-vortex array. Depending on initial kinematic conditions, two different Ar structures are found: either a compact, gas-phase like cluster, or a loosely bound metastable cluster with helium density caged inside. In the presence of the vortex array, the argon atoms are deflected by the superfluid flow, tending to orbit around the vortex cores. The Ar atoms end up being trapped together in a loosely bound structure attached to the central vortex core.