Theory of mechanical spin current generation via spin–rotation coupling

The spin–rotation coupling (SRC) is responsible for angular momentum conversion between the electron spin and rotational deformations of elastic media, whereby spin current generation from mechanical motions is theoretically predicted. Here a surface acoustic wave (SAW) is considered as an example of such elastic deformations. We formulate the spin diffusion equation that is extended to include the influence of the SRC, and from the solution we find that larger spin currents can be obtained in materials with longer spin lifetimes. This distinct feature arises from the fact that the present method is of “purely” mechanical origin, i.e., it relies on neither equilibrium magnetization nor spin–orbit coupling, offering a new route to building the so-called “rare-metal-free” spintronics devices.