Berry Phase and Ground State Symmetry in H x h Dynamical Jahn-Teller Systems

TL;DR

This paper investigates how the Berry phase influences the symmetry of the vibronic ground state in dynamical Jahn-Teller systems, highlighting an exception in the H x h icosahedral model relevant to C60 cations.

Contribution

It identifies a unique tunable parameter in the H x h model that can remove the Berry phase, altering the ground state symmetry from degenerate to nondegenerate.

Findings

Berry phase typically preserves ground state symmetry in Jahn-Teller systems

The H x h model can be tuned to eliminate the Berry phase

Removing the Berry phase changes the ground state to nondegenerate

Abstract

Due to the ubiquitous presence of a Berry phase, in most cases of dynamical Jahn-Teller systems the symmetry of the vibronic ground state is the same as that of the original degenerate electronic state. As a single exception, the linear H x h icosahedral model, relevant to the physics of C60 cations, is determined by an additional free parameter, which can be continuously tuned to eliminate the Berry phase from the low-energy closed paths: accordingly, the ground state changes to a totally-symmetric nondegenerate state.