Nonequilibrium spin density and spin-orbit torque in a three-dimensional topological insulator/antiferromagnet heterostructure

We study the behavior of nonequilibrium spin density and spin-orbit torque in a topological insulator/antiferromagnet heterostructure. Unlike ferromagnetic heterostructures where the Dirac cone is gapped due to time-reversal symmetry breaking, here the Dirac cone is preserved. We demonstrate the existence of a staggered spin density corresponding to a dampinglike torque which is quite robust against scalar impurities when the transport energy is such that the transport is confined to the topological insulator surface. We show the contribution to the nonequilibrium spin density due to both surface and bulk topological insulator bands. Finally, we show that the torques in topological insulator/antiferromagnet heterostructures exhibit an angular dependence that is consistent with the standard spin-orbit torque obtained in Rashba system with some additional structure arising from the interfacial coupling.