Spintronics at Nanoscale: Flat-Band Ferromagnetism in Armchair   Nanoribbons and Nanotubes
  We study the electronic correlation effects in armchair nanoribbon and nanotube using weak-coupling approach and non-Abelian density-matrix renormalization-group method. We show that upon appropriate doping, the system exhibits a new type of flat-band ferromagnetism, different from the well-known Milke-Tasaki one. The strongly correlated ground state consists of intrinsic magnetic moments of flat-band states and itinerant carriers of dispersive bands, and the exchange coupling between them yields a ferromagnetism. The resultant ferromagnetic state with metallic conductivity has a potential in spintronics applications at nanoscale. 
Hsiu-Hau Lin, Toshiya Hikihara, Bor-Lung Huang, Chung-Yu Mou, Xiao Hu