Acoustic generation of orbital currents

In solids, the crystal field couples the electronic orbital degree of freedom to the lattice. This coupling suggests that an excitation of lattice dynamics could trigger the dynamics of orbital angular momentum of electrons, thereby generating orbital currents—a flow of electronic orbital angular momentum. However, the interplay between orbital currents and lattice dynamics has been elusive. Here, we report the observation of the acoustic orbital Hall effect, demonstrating the generation of orbital currents by lattice dynamics. By investigating the acoustoelectric properties of Ti/Ni bilayers induced by surface acoustic waves (SAWs), we demonstrate the generation of an orbital current polarized transverse to the SAW propagation direction. This phenomenon is reminiscent of the electric orbital Hall effect, which generates an orbital current polarized transverse to an applied electric field. We also show that acoustically driven ferromagnetic resonance generates an orbital current in the Ti/Ni bilayer, demonstrating acoustic orbital pumping. These findings highlight the potential of lattice dynamics in generating orbital currents, paving the way for exploring acoustic orbitronics. The orbital Hall effect has recently been shown to produce orbital torques, allowing for the efficient driving of magnetization by light metals such as titanium. Here, Taniguchi et al show that orbital currents can also be generated by surface acoustic waves, showing this in a titanium/nickel bilayer.