The role of orbital polarization and spin-dependent electron-phonon scatterings in chiral-induced spin selectivity

Chiral materials exhibit unique spin and charge transport properties, notably through the chiral induced spin selectivity (CISS) effect, enabling spin-polarized currents in nonmagnetic materials without external magnetic fields at room temperature. In this study, we investigate the microscopic mechanisms underlying CISS in a prototypical chiral solid, trigonal selenium (Se), based on a first principles spatial-temporal resolved density-matrix dynamics approach, including electron-phonon scattering with self-consistent spin-orbit couplings (SOC). Our approach elucidates the interplay of SOC, structural chirality, and spin-dependent electron-phonon interactions in driving the generation and transport of spin and orbital angular momentum. We demonstrate that charge transport along the chiral axis induces significant chirality-dependent spin and orbital polarization, which shows a monotonic increase with higher chirality. Meanwhile, we show the orbital polarization generated in CISS has a weak dependence on SOC, unlike spin. Most importantly, we reveal the key difference between the CISS and colinear Edelstein effect (CEE) originating from spin-dependent electron-phonon scatterings, which explains the spin polarization increase with device lengths, a unique feature in CISS.