Lossless Spin-Orbit Torque in Antiferromagnetic Topological Insulator MnBi2Te4

We formulate and quantify the spin-orbit torque (SOT) in intrinsic antiferromagnetic topological insulator ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$ of a few septuple-layer thick in charge-neutral condition, which exhibits pronounced layer-resolved characteristics and even-odd contrast. Contrary to traditional current-induced torques, our SOT is not accompanied by Ohm’s currents, thus being devoid of Joule heating. We study the SOT-induced magnetic resonances, where in the tri-septuple-layer case we identify a peculiar exchange mode that is blind to microwaves but can be exclusively driven by the predicted SOT. As an inverse effect, the dynamical magnetic moments generate a pure adiabatic current, which occurs concomitantly with the SOT and gives rise to an overall reactance for the ${\mathrm{MnBi}}_2{\mathrm{Te}}_4$, enabling a lossless conversion of electric power into magnetic dynamics.