  A graphene nanoribbon (GNR) with orientation along its principle axis was
obtained through a mechanical tearing process, and a quantum dot device was
fabricated from the GNR. We have studied the transport property of the GNR
quantum dot device down to dilution refrigerator temperatures. Two-fold
charging periodicity was observed in the Coulomb-blockade measurement,
signaling a shell-filling process with broken valley degeneracy. In one of the
smaller Coulomb diamonds, Kondo-like resonance were observed, with two
conductance peaks displaced symmetrically from the zero bias voltage. The
splitting of Kondo resonance at zero magnetic field suggests spin-polarization
of the quantum dot, possibly due to the edge states of a zigzag GNR.
