▎ 摘　　要

We demonstrate that the direction of transverse current in graphene nanoribbons under a magnetic field can be tuned with a gate voltage. It is shown that for armchair ribbons there exist extra energy regions where the direction of the Hall current can be switched between positive and negative values. The directional change of the Hall current coincides with the special points where the two lowest energy bands in the spectrum become degenerate (band crossing points). The number of such degenerate points depends on the width of the ribbons. The dependence of the sign reversal on the gate voltage provides a mechanism for tuning transverse response in graphene based devices. (C) 2011 American Institute of Physics. [doi:10.1063/1.3622323]