  Organic/inorganic interfaces formed by monolayer substrates and conjugated
molecular adsorbates are attractive material platforms leveraging the
modularity of organic compounds together with the long-range phenomena typical
of condensed matter. New quantum states are known to be generated by electronic
interactions in these systems as well as by their coupling with light. However,
little is still known about hybrid vibrational modes. In this work, we discover
from first principles the existence of an infrared-active chiral phonon mode in
a pyrene-decorated MoSe$_{2}$ monolayer given by the combination of a
frustrated rotation of the molecule around its central axis and an optical mode
in the substrate. Our results suggest the possibility to enable phonon
chirality in molecular superlattices.
