Emergence of Dirac half-semimetallic channels in graphene nanoribbon/hexagonal boron nitride heterojunctions

Materials hosting half-metallic phases are envisioned as active components in spintronic devices owing to their fully spin-polarized electrical currents, yet their deployment is limited by their scarcity. Here, using first-principles calculations and model Hamiltonians, we predict that recently fabricated heterojunctions of zigzag graphene nanoribbons embedded in two-dimensional hexagonal boron nitride are half-semimetallic, featuring Dirac points at the Fermi level. The Dirac half-semimetallicity originates from the transfer of ambipolar charges from hexagonal boron nitride to the embedded graphene nanoribbon. Upon charge doping, an antiferromagnetic-to-ferrimagnetic phase transition occurs in these heterojunctions, with the sign of the excess charge governing the spatial localization of the net magnetic moments. Our findings demonstrate that such heterojunctions realize one-dimensional conducting channels of spin-polarized Dirac fermions integrated into a two-dimensional insulator, thus holding promise for the development of carbon-based spintronics.