Giant Response and Harmonic Generation in N\'eel-Torque Antiferromagnetic Resonance

Abstract

We theoretically investigate the resonant and higher order 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 terahertz frequency range. From the effective dynamics, we uncover the strong coupling between the N\'eel vector and the driving field of NSOTs, providing a physical explanation of the gigantic responses at all orders. 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.