  Brillouin zones of graphene systems possess Dirac points, where band
degeneracies occur. We study the variety of (and large magnitude) phases that
the electronic states can acquire when a uniform time-dependent electric field
carries the electrons around one or more Dirac points in a non-concentric
fashion. An experimentally accessible determination of excess Berry phases is
proposed involving the Zitterbewegung of electronic current near an
orthogonality point in adiabatic motion.
