Topological Dirac Spin-Gapless Materials -- New Horizon for Topological Spintronics Without Spin-Orbit Interaction

The existence of chiral edge states, corresponding to the nontrivial bulk-band topology characterized by a non-vanishing topological invariant, and the manipulation of topological transport via chiral edge states promise topological electronic/spintronic device applications. Here we predict the existence, practical realization, topological protection, and topological switching of spin-gapless valley-filtered chiral edge states, representing a novel topological Dirac spin-gapless/half-metal phase in antiferromagnetic honeycomb structures terminated on zigzag edges. We demonstrate that this phenomenon is realizable if a perpendicular (transverse) electric field is applied in zigzag nanoribbons with an antiferromagnetic ordering on the boundary (in the bulk), and the Weber-Fechner type nonlinear behavior is optimizable by a transverse (perpendicular) electric field. The existence of spin-gapless valley-filtered chiral edge states, their correspondence with nontrivial topological character in the bulk, and electric-field-driven switching of their spin-polarization that is accompanied by switching of bulk-band topology promise a new strategy for topological spintronics without spin-orbit interaction.