Direct observation of the reciprocity between spin current and phonon interconversion

Spin current has emerged as a leading candidate for manipulation of spins in a nano-magnet. We here experimentally show another utility of spin current, viz., it can be used for the generation of phonons. Within the same experimental setup, we also demonstrate the inverse effect of generation of spin current by phonons. To demonstrate these effects, we measured the scattering-matrix of a two-port device with interdigital transducers as one port and an array of Ni/Pt lines as a second port made on a piezoelectric substrate. The off-diagonal elements which correspond to transmission between the ports were found to have 180° relative phase shift. The transmission of electrical signals from port 2 to 1 corresponds to the generation of phonons from spin-current, while transmission from port 1 to 2 corresponds to the inverse effect. These results could be useful for designing spin-current based gyrators. We further show the reciprocity between spin transfer torque and spin pumping effects.