Charge current-induced collinear spin polarization: chiral conductors versus chiral insulators

Generation of electronic spin polarization in nonmagnetic materials without an external magnetic field is of broad interest in spintronics and quantum information science. Chiral systems provide a promising route toward this goal, where real-space structural chirality leads to charge current-induced collinear spin polarization. One well-established mechanism is the collinear Rashba-Edelstein effect (c-REE) in conductive chiral materials, in which the Weyl-type spin–orbit coupling results in radial hedgehog spin texture on the Fermi surface, thus a charge current produces a spin accumulation polarized collinearly with the carrier momentum. A conceptually different route emerges in insulating chiral media, e.g. chiral molecules, where chirality-induced spin selectivity (CISS) manifests as spin-dependent transmission of charge carriers. We have measured and analyzed the magnetoconductance of molecular spin-valves comprising a normal metal electrode, a chiral molecule monolayer barrier, and ferromagnetic semiconductor spin analyzer. The results are well accounted for by a model based on magnetochiral modulation of the tunneling barrier. The observations demonstrate that despite their phenomenological similarities, mechanistically CISS differs fundamentally from c-REE. Our results highlight CISS-based tunneling structures as a distinct nonmagnetic platform for charge-spin conversion.