Itinerant half-metal spin-density-wave state on the hexagonal lattice

We consider electrons on a honeycomb or triangular lattice doped to the saddle point of the band structure. We assume the system parameters are such that spin density wave (SDW) order emerges below a temperature T _N and investigate the nature of the SDW phase. We argue that at T≤T _N, the system develops a uniaxial SDW phase whose ordering pattern breaks O(3)×Z ₄ symmetry and corresponds to an eight-site unit cell with nonuniform spin moments on different sites. This state is a half-metal-it preserves the full original Fermi surface, but has gapless charged excitations in one spin branch only. It allows for electrical control of spin currents and is desirable for nanoscience.