Half metallicity along the edge of zigzag boron nitride nanoribbons

First-principles calculations within the local spin-density approximation reveal half metallicity in zigzag boron nitride nanoribbons (ZBNNRs). When the B edge, but not the N edge, of the ZBNNR is passivated, despite being a pure $sp$-electron system, the ribbon shows a giant spin splitting. The electrons at the Fermi level are 100% spin polarized with a half-metal gap of 0.38 eV and its conductivity is dominated by metallic single-spin states. The two states crossing at the Dirac point have different molecular origins, which signal a switch of carrier velocity. The ZBNNR should be a good potential candidate for wide gap spintronics.