Role of Polaron Spin State in Chirality-Induced Spin Selectivity

The fundamental origin of the pronounced spin polarization observed in chirality-induced spin selectivity (CISS) remains an open question. Using the well-established Lee-Low-Pines unitary transformation framework, we investigated polaron spin states in chiral systems under weak and strong electron-phonon coupling regimes. Our calculations reveal that the strain tensor, induced by phonon displacements in chiral structures, directly interacts with electron spins. Notably, we observed a significant increase in the splitting magnitude of polaron spin states with the rise in the cutoff wavevector of phonon modes. These findings suggest that phonon displacements within chiral structures amplify spin-orbit coupling, enhancing spin filtering during electron transport through the chiral medium. This study provides critical insights into the polaron spin states in chiral systems, contributing to understanding the phonon-assisted CISS mechanism.