Nonreciprocal Pumping of Phonon Spin by Magnetization Dynamics

We propose a method to control surface phonon transport by weak magnetic fields based on the theory of nonreciprocal pumping of surface acoustic waves (SAWs) by magnetostriction. We predict that the magnetization dynamics of a nanowire on top of a dielectric films pumps SAWs with opposite angular momenta into opposite directions, thus generating unidirectional phonon spin transport. Two parallel nanowires form a phononic cavity that at geometrical resonances pump a unidirectional SAW current into half of the substrate.