Inverse Acoustic Spin Hall Effect in Heavy Metal-Ferromagnet Bilayers

The acoustic spin Hall effect (ASHE) enables the generation of spin current via lattice vibrations driven by surface acoustic waves (SAWs) in heavy metals. Here, we report its reciprocal counterpart—the inverse ASHE—in which an alternating (ac) spin current induces coherent lattice vibrations that propagate SAWs. By injecting ac spin currents into a heavy metal via interfacial spin backflow in a heavy metal-ferromagnet bilayer, we successfully detect such spin-current-induced nonlocal SAWs over distances up to 400μm in an LiNbO3 substrate. As the previously unobserved reciprocal element in spin-lattice interactions, the inverse ASHE completes the framework of spin-phonon interconversion and uncovers a phonon-mediated pathway for long-range spin transport, even through nonmagnetic insulators.