In this work, using self-consistent tight-binding calculations, for the first
time, we show that a direct to indirect bandgap transition is possible in an
armchair graphene nanoribbon by the application of an external bias along the
width of the ribbon, opening up the possibility of new device applications.
With the help of Dirac equation, we qualitatively explain this bandgap
transition using the asymmetry in the spatial distribution of the perturbation
potential produced inside the nanoribbon by the external bias. This is followed
by the verification of the bandgap trends with a numerical technique using
Magnus expansion of matrix exponentials. Finally, we show that the carrier
effective masses possess tunable sharp characters in the vicinity of the
bandgap transition points.Comment: Accepted for publication in Nano Letter
