Berry Phase and the Symmetry of the Vibronic Ground State in Dynamical Jahn-Teller Systems

TL;DR

This paper explores how Berry phases influence the symmetry of the vibronic ground state in dynamical Jahn-Teller systems, revealing cases where symmetry changes occur at strong coupling, especially in icosahedral systems relevant to fullerene ions.

Contribution

It generalizes the understanding of Berry phase effects on ground state symmetry, including examples where absence of Berry phase does not imply degeneracy.

Findings

In most dynamical Jahn-Teller systems, Berry phase preserves ground state symmetry.

In icosahedral systems, strong coupling can lead to symmetry change due to linear coupling.

Absence of Berry phase does not necessarily result in a nondegenerate ground state.

Abstract

Due to the frequent presence of a Berry phase, in most cases of dynamical Jahn-Teller systems the symmetry of the ground state is the same as that of the electronic state. However, the H x h icosahedral case, relevant for the physics of fullerene ions, provides a first example of linear coupling leading, at strong coupling, to a change in symmetry of the ground state to a totally symmetric nondegenerate state. We generalize this observation and show through detailed examples that the absence of a Berry phase can, but does not necessarily, lead to a nondegenerate ground state.