Quasiparticle approach to molecules interacting with quantum solvents

TL;DR

This paper demonstrates that molecules in superfluid helium form angulon quasiparticles, simplifying the complex many-body problem and aligning well with experimental data, thus advancing understanding of molecular rotation in quantum solvents.

Contribution

It provides experimental evidence for angulon quasiparticles in molecules within superfluid helium and offers an analytic approach to determine molecular moments of inertia.

Findings

Good agreement between angulon theory and experiments across various molecular species.

Simplification of the many-body problem using angulon quasiparticles.

Analytic solutions for effective molecular moments of inertia.

Abstract

Understanding the behavior of molecules interacting with superfluid helium represents a formidable challenge and, in general, requires approaches relying on large-scale numerical simulations. Here we demonstrate that experimental data collected over the last 20 years provide evidence that molecules immersed in superfluid helium form recently-predicted angulon quasiparticles [Phys. Rev. Lett. 114, 203001 (2015)]. Most importantly, casting the many-body problem in terms of angulons amounts to a drastic simplification and yields effective molecular moments of inertia as straightforward analytic solutions of a simple microscopic Hamiltonian. The outcome of the angulon theory is in good agreement with experiment for a broad range of molecular impurities, from heavy to medium-mass to light species. These results pave the way to understanding molecular rotation in liquid and crystalline phases in terms of the angulon quasiparticle.