Effects of the nearest neighbor Coulomb interaction on nanographene ribbons
with zigzag edges are investigated using the extended Hubbard model within the
unrestricted Hartree-Fock approximation. The nearest Coulomb interaction
stabilizes a novel electronic state with the opposite electric charges
separated and localized along both edges, resulting in a finite electric dipole
moment pointing from one edge to the other. This charge-polarized state
competes with the peculiar spin-polarized state caused by the on-site Coulomb
interaction and is stabilized by an external electric field.Comment: 4 pages; 4 figures; accepted for publication in Phys. Rev. B; related
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