Acoustic spin Hall effect in strong spin-orbit metals

TL;DR

This paper demonstrates the acoustic spin Hall effect in strong spin-orbit metals, showing how lattice vibrations can generate spin currents via spin-orbit interaction, with potential implications for spintronics.

Contribution

It reports the first observation of the acoustic spin Hall effect driven by surface acoustic waves in non-magnetic metals with strong spin-orbit interaction.

Findings

Spin current flows orthogonal to SAW propagation in non-magnetic metals.

Maximum acoustic voltage occurs when NM layer thickness matches spin diffusion length.

Spin current scales with SOI strength and lattice displacement derivative.

Abstract

We report on the observation of the acoustic spin Hall effect that facilitates lattice motion induced spin current via spin orbit interaction (SOI). Under excitation of surface acoustic wave (SAW), we find a spin current flows orthogonal to the propagation direction of a surface acoustic wave (SAW) in non-magnetic metals. The acoustic spin Hall effect manifests itself in a field-dependent acoustic voltage in non-magnetic metal (NM)/ferromagnetic metal (FM) bilayers. The acoustic voltage takes a maximum when the NM layer thickness is close to its spin diffusion length, vanishes for NM layers with weak SOI and increases linearly with the SAW frequency. To account for these results, we find the spin current must scale with the SOI and the time derivative of the lattice displacement. Such form of spin current can be derived from a Berry electric field associated with time varying Berry curvature and/or an unconventional spin-lattice interaction mediated by SOI. These results, which imply the strong coupling of electron spins with rotating lattices via the SOI, show the potential of lattice dynamics to supply spin current in strong spin orbit metals.