  First-principles density functional calculations are performed in C-BN
heterojunctions. It is shown that the magnetism of the edge states in zigzag
shaped graphene strips and polarity effects in BN strips team up to give a spin
asymmetric screening that induces half-semimetallicity at the interface, with a
gap of at least a few tenths of eV for one spin orientation and a tiny gap of
hundredths of eV for the other. The dependence with ribbon widths is discussed,
showing that a range of ribbon widths is required to obtain
half-semimetallicity. These results open new routes for tuning electronic
properties at nanointerfaces and exploring new physical effects similar to
those observed at oxide interfaces, in lower dimensions.
