  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.

Mesoscale and Nanoscale Physics