  Graphene nanoribbons with zigzag terminated edges have a magnetic ground
state characterized by edge ferromagnetism and antiferromagnetic inter edge
coupling. This broken symmetry state is degenerate in the spin orientation and
we show that, associated with this degeneracy, the system has topological
solitons. The solitons appear at the interface between degenerate ground
states. These solitons are the relevant charge excitations in the system. When
charge is added to the nanoribbon, the system energetically prefers to create
magnetic domains and accommodate the extra electrons in the interface solitons
rather than setting them in the conduction band.
