Theory of spin Seebeck effect activated by acoustic chiral phonons

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 response induced by microscopic acoustic-phonon-mediated lattice rotation, we derive a formula for the spin current when a finite temperature difference is imposed between two ends of the sample. We clarify how the phonon-mediated 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 or spin–orbit interactions. • Microscopic theory for spin current generation in CI-NM junction by thermal gradient. • The mechanism based on the gyromagnetic response induced by lattice rotation. • Chiral-phonon-driven spin Seebeck effect without magnetism or spin-orbit coupling.