Aggregation of solutes in bosonic versus fermionic quantum fluids.

Area of Science:

• * Quantum physics
• * Atomic and molecular physics
• * Condensed matter physics

Background:

• * Helium-3 (³He) and helium-4 (⁴He) droplets are utilized as cryogenic nanolaboratories.
• * They were presumed to offer a homogeneous environment for ultracold chemistry and spectroscopy.
• * Dopants were expected to behave as if in free space at near-absolute-zero temperatures.

Purpose of the Study:

• * To investigate the internal structure and dopant distribution in xenon-doped ³He and ⁴He nanodroplets.
• * To determine the effect of droplet dynamics on dopant behavior.
• * To challenge the prevailing assumption of homogeneous environments in superfluid nanodroplets.

Main Methods:

• * Ultrafast x-ray diffraction experiments were performed on superfluid ³He and ⁴He nanodroplets doped with xenon.
• * Analysis focused on the structural arrangements of dopants within the droplets.

Main Results:

• * Rotational excitation of the droplets leads to anisotropic and inhomogeneous dopant interactions.
• * In superfluid ⁴He droplets, quantum vortices trap dopants, forming filament-shaped clusters.
• * In ³He droplets, dopants aggregate into diffuse, ring-shaped structures along the equator.

Conclusions:

• * The observed filament and ring structures are direct evidence of inhomogeneous dopant distributions.
• * Rotational excitation is identified as the primary cause for these non-uniform dopant arrangements.
• * The cryogenic nanolaboratory concept needs re-evaluation due to these dynamic effects.