Chiral Phonon Activated Spin Seebeck Effect

Abstract: Efficient generation of spin polarization is the central focus of spintronics. In magnetic materials, spin currents can arise from heat currents by the conventional spin Seebeck effect. Recently, chiral phonons with definite handedness and angular momenta have also produced profound impacts on multiple research fields. In this paper, starting with nonequilibrium distribution of chiral phonons under temperature gradient, we find a new spin selectivity effect - chiral phonon activated spin Seebeck (CPASS) effect, in chiral materials without magnetic order nor spin-orbit coupling. With both phonon-drag and band transport contributions, the CPASS coefficients are computed based on the Boltzmann transport theory. The spin accumulations by the CPASS effect quadratically increase with temperature gradient, and vary with the chemical potential modulation, thus enabling highly efficient and tunable spin generation. The CPASS effect provides a promising explanation on the chiral-induced spin selectivity effect and opportunities for designing advanced spintronic devices based on nonmagnetic chiral materials.