  We investigate magneto-transport through graphene nano-ribbons as a function
of gate and bias voltage, and temperature. We find that a magnetic field
systematically leads to an increase of the conductance on a scale of a few
tesla. This phenomenon is accompanied by a decrease in the energy scales
associated to charging effects, and to hopping processes probed by
temperature-dependent measurements. All the observations can be interpreted
consistently in terms of strong-localization effects caused by the large
disorder present, and exclude that the insulating state observed in
nano-ribbons can be explained solely in terms of a true gap between valence and
conduction band.
