  It is shown that a graphene ribbon, a ballistic strip of carbon monolayer,
may serve as a quantum wire whose electronic properties can be continuously and
reversibly controlled by an externally applied transverse voltage. The electron
bands of armchair-edge ribbons undergo dramatic transformations: The Fermi
surface fractures, Fermi velocity and effective mass change sign, and
excitation gaps are reduced by the transverse field. These effects are manifest
in the conductance plateaus, van Hove singularities, thermopower, and activated
transport. The control over one-dimensional bands may help enhance effects of
electron correlations, and be utilized in device applications.
