Intrinsic vibrational angular momentum from non-adiabatic effects in non-collinear magnetic molecules

TL;DR

This paper reveals that non-adiabatic effects in non-collinear magnetic molecules induce a geometric vector potential, leading to intrinsic vibrational angular momentum that can be significant and observable.

Contribution

It introduces the concept of non-adiabatic effects causing intrinsic vibrational angular momentum via Berry connection in non-collinear magnetic molecules, supported by first-principles calculations.

Findings

Non-adiabatic effects break time-reversal symmetry in vibrational modes.

Vibrational modes can carry sizeable intrinsic angular momentum.

First-principles calculations show angular momentum comparable to electronic orbital moments.

Abstract

We show that in non-collinear magnetic molecules, non-adiabatic (dynamical) effects due to the electron-vibron coupling are time-reversal symmetry breaking interactions for the vibrational field. As in these systems the electronic wavefunction can not be chosen as real, a nonzero geometric vector potential (Berry connection) arises. As a result, an intrinsic nonzero vibrational angular momentum occurs even for non-degenerate modes and in the absence of external probes. The vibronic modes can then be seen as elementary quantum particles carrying a sizeable angular momentum. As a proof of concept, we demonstrate the magnitude of this topological effect by performing non-adiabatic first principles calculations on platinum clusters and by showing that these molecules host sizeable intrinsic phonon angular momenta comparable to the orbital electronic ones in itinerant ferromagnets.