Description
Acoustic spintronics exploits surface acoustic waves to control spin dynamics, yet research has largely been confined to linear magnon-phonon coupling in ferromagnets. Extending this to the nonlinear regime and to antiferromagnetic materials—which promise terahertz operation and are free from stray fields—remains a formidable challenge. Here, we report the first observation of two-phonon antiferromagnetic resonance and the demonstration of two-phonon-assisted acoustic spin pumping in an antiferromagnet. We theoretically show that including higher-order terms of the strain tensor in the magnetoelastic interaction Hamiltonian leads to a nonlinear two-phonon absorption process, which becomes dominant when the local phonon energy density is sufficiently high. We experimentally validate this prediction using focused interdigital transducers to locally enhance the phonon density in the van der Waals antiferromagnet chromium trichloride (CrCl3), thereby observing distinct two-phonon absorption signatures in acoustic antiferromagnetic resonance. Furthermore, by resonantly driving the acoustic magnon mode of CrCl3, we achieve acoustic antiferromagnetic spin pumping, generating pure spin currents detected via the inverse spin Hall effect. These pure direct current (DC) spin signals additionally confirm the existence of the two-phonon absorption process. Our work unveils a nonlinear pathway for high-frequency magnon control using low-frequency acoustic waves and opens an avenue for acoustic antiferromagnetic spintronic devices.
