Parity law of the singlet-triplet gap in graphitic ribbonsM. Al Hajj, F. Alet, S. Capponi, M. B. Lepetit, J.-P. Malrieu and S. TodoEur. Phys. J. B, 51 4 (2006) 517-522DOI: https://doi.org/10.1140/epjb/e2006-00259-9