BERRY PHASE AND THE GAMMA-8X(TAU-2+EPSILON) JAHN-TELLER SYSTEM

The ground-state Berry phase of the GAMMA(8) x (tau(2) + epsilon) Jahn-Teller system in strong coupling is calculated, for both equal and unequal couplings to the phonon modes. Because of time-reversal invariance and the resulting degeneracy in the states, the usual Berry-phase analysis for the time evolution of nondegenerate states must be augmented by the generalized formalism of Wilczek and Zee. In the GAMMA(8) x (tau(2) + epsilon) system, the Berry-phase factor becomes a 2 x 2 unitary matrix. Explicit analytical expressions for the ground states are derived.