High-Efficiency Spin-Orbit Torque in Antiferromagnetic Topological Insulator MnBi2Te4

We formulate and quantify the spin-orbit torque (SOT) in intrinsic antiferromagnetic topological insulator MnBi2Te4 of a few septuple-layer (SL) thick, which arises from electric fields (or voltages) rather than charge currents and exhibits a conspicuous even-odd SL-number pattern. The predicted SOT is demonstrated in the SOT-driven magnetic resonance, where we identify a peculiar exchange mode in the tri-SL case that is blind to microwave electromagnetic fields but can only be excited by the SOT. As the reciprocal effect of the SOT, topological charge pumping generates an adiabatic current devoid of Joule heating with the onset of exchange resonance. Thanks to the absence of charge currents, MnBi2Te4 can be operated as an adiabatic quantum motor through pure voltage drives, achieving a theoretical mechanical efficiency of 100%.