Gigantic Harmonic Generation in Néel-Torque Antiferromagnetic Resonance

Abstract: We theoretically investigate the resonant and higher-harmonic magnetic responses of a collinear antiferromagnet induced by N\'eel spin-orbit torques (NSOTs). By deriving the dynamical susceptibilities up to the third harmonic, we find remarkable NSOT-induced amplifications of the linear and nonlinear magnetic dynamics by orders of magnitude compared to conventional spin-orbit torques, enabling highly-efficient frequency conversion in the sub-terahertz frequency range. We then propose a multilayer antiferromagnetic nano-device leveraging the gigantic harmonic generation to achieve unprecedented frequency amplifiers and converters. Our work uncovers a previously overlooked role of the NSOTs in nonlinear dynamics.