Libration of strongly-oriented polar molecules inside a superfluid

TL;DR

This paper investigates how a polar molecule's librational motion inside a superfluid is affected by an external electrostatic field, revealing new quasiparticle states called pendulons and their tunable instabilities.

Contribution

It introduces the concept of pendulons, showing how external fields can control molecular rotational instabilities in superfluid environments.

Findings

Pendulons are spherical harmonic librators dressed by many-particle excitations.

External fields can tune the positions of spectral instabilities.

Spectral features differ significantly from the field-free angulon case.

Abstract

We study a polar molecule immersed into a superfluid environment, such as a helium nanodroplet or a Bose-Einstein condensate, in the presence of an intense electrostatic field. We show that coupling of the molecular pendular motion, induced by the field, to the fluctuating bath leads to formation of pendulons -- spherical harmonic librators dressed by a field of many-particle excitations. We study the behavior of the pendulon in a broad range of molecule-bath and molecule-field interaction strengths, and reveal that its spectrum features series of instabilities which are absent in the field-free case of the angulon quasiparticle. Furthermore, we show that an external field allows to finetune the positions of these instabilities in the molecular rotational spectrum. This opens the door to detailed experimental studies of redistribution of orbital angular momentum in many-particle systems.