Theory of chiral-phonon-activated spin Seebeck effect

Abstract: We theoretically explore the generation of spin current driven by a temperature gradient in a junction between a chiral insulator and a normal metal. Based on the gyromagnetic effect caused by microscopic rotation due to phonons, we derive a formula for a spin current when a finite temperature difference is imposed at two ends of the sample. We clarify how the spin current depends on the sample geometry, the thermal conductivity, the heat conductance at the interface, and the average temperature. Our formulation provides a microscopic foundation for the chiral-phonon-activated spin Seebeck effect without relying on magnetism and spin-orbit interactions.