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Spin-valley half-metal in systems with Fermi surface nesting
Half-metals have fully spin-polarized charge carriers at the Fermi surface. Such polarization usually occurs due to strong electron-electron correlations. Recently [Phys. Rev. Lett. 119, 107601 (2017)] we have demonstrated theoretically that adding (or removing) electrons to systems with Fermi surface nesting also stabilizes
the half-metallic states even in the weak-coupling regime. In the absence of doping, the ground state of the
system is a spin or charge density wave, formed by four nested bands. Each of these bands is characterized by
charge (electron/hole) and spin (up/down) labels. Only two of these bands accumulate charge carriers introduced
by doping, forming a half-metallic two-valley Fermi surface. Analysis demonstrates that two types of such
half-metallicity can be stabilized. The first type corresponds to the full spin polarization of the electrons and holes
at the Fermi surface. The second type, with antiparallel spins in electronlike and holelike valleys, is referred to as
a “spin-valley half-metal” and corresponds to the complete polarization with respect to the spin-valley operator.
We analyze spin and spin-valley currents and possible superconductivity in these systems. We show that spin or
spin-valley currents can flow in half-metallic phases.