Two-dimensional spin-valley-coupled Dirac semimetals in functionalized SbAs monolayers

In the presence of spin-orbit coupling (SOC), achieving both spin and valley polarized Dirac states is significant to promote the fantastic integration of Dirac physics, spintronics and valleytronics. Based on ab initio calculations, here we demonstrate that a class of spin-valley-coupled Dirac semimetals (svc-DSMs) in functionalized SbAs monolayers (MLs) can host such desired states. Distinguished from the graphene-like 2D Dirac materials, Dirac cones in svc-DSMs hold giant spin-splitting induced by strong SOC under inversion symmetry breaking. In 2.3% strained SbAsH₂ MLs, Dirac fermions in inequivalent valleys have opposite Berry curvature and spin moment, giving rise to a Dirac spin-valley Hall effect with constant spin Hall conductivity as well as massless and dissipationless transport. Topological analysis reveals that the svc-DSM emerges at the boundary between trivial and 2D topological insulators, which provides a promising platform for realizing flexible and controllable tuning among different quantum states.