Chirality-Induced Spin Selectivity: Nonlinear Spin Response from Electron-Phonon Scattering

TL;DR

This paper uses first-principles simulations to clarify how electron-phonon interactions and spin-orbit coupling in chiral materials produce nonlinear spin responses characteristic of CISS, distinguishing it from other effects.

Contribution

It provides a microscopic understanding of CISS by explicitly modeling spin-dependent electron-phonon interactions and their nonlinear effects in chiral solids.

Findings

CISS produces a nonlinear spin response scaling as E^2.

Intervalley scattering mediated by chiral phonons is key to CISS.

CISS differs from the Edelstein effect in its spatial and field dependence.

Abstract

Chirality-induced spin selectivity (CISS) generates spin-polarized currents in nonmagnetic materials from structural chirality alone, yet its microscopic origin remains debated. Using a first-principles spatiotemporal density-matrix dynamics approach including electron-phonon scatterings with self-consistent spin-orbit coupling (SOC), we elucidate the interplay of SOC, structural chirality, and spin-dependent electron-phonon interactions in driving the generation and transport of spin and orbital angular momentum. In particular we quantitatively distinguish CISS from the collinear Edelstein effect (CEE) in trigonal selenium, a prototypical chiral solid. CEE yields a spatially uniform spin polarization scaling linearly with applied field ($S_z \propto E$). In contrast, explicit spin-dependent electron-phonon scattering produces a nonlinear response ($S_z \propto E^2$) and a length-dependent spin accumulation -- the hallmark experimental signature of CISS. We identify intervalley scattering mediated by chiral phonon angular momentum as the microscopic origin of this nonlinearity.