Spin-orbit coupling and beyond in Chiral-Induced Spin Selectivity

Abstract

Chiral-Induced Spin Selectivity (CISS) describes the emergence of spin-polarized electron transport in chiral systems without magnetic fields, a remarkable effect in light-element materials with weak intrinsic spin-orbit coupling (SOC). This mini-review analyzes the microscopic origins of CISS, highlighting how molecular chirality, local electric fields, and dynamic distortions enhance effective SOC and drive spin-dependent transport. We critically assess existing models in terms of their symmetry constraints, phenomenological assumptions, and compliance with Onsager reciprocity. Recent developments combining relativistic quantum mechanics and complete multipole representations reveal a direct link between chirality density and spin current pseudoscalars, suggesting a field-theoretic foundation for CISS. These insights could help position light-element chiral nanomaterials as tunable platforms for probing and engineering spin-selective phenomena at the nanoscale.

Figures (5)

• Figure 1: Selection of various phenomena that can be traced back to CISS. (A) Schematic of a dsDNA monolayer as a spin filter: unpolarized electrons ejected from Au by linearly polarized light become spin-polarized antiparallel to their velocity, while non-transmitted electrons tunnel back to the substrate. (B) Energy scheme of $|{\rm momentum, spin}\rangle$ states in a chiral potential; spin flips with helix handedness. (C) Charge $q$ in spin state $\sigma$ moving along a helical charge distribution (pitch $p$, radius $R$, spacing $\Delta z$); the helical field $\vec{E}_{\rm helix}$ induces $\vec{B}$ affecting spin. (D) Spin polarization of photoelectrons from Au(111) with cw (green), ccw (red), and linear (blue) light ($-22\%$, $+22\%$, $0\%$, respectively); dsDNA/Au(111) transmits spin-polarized electrons. (E) $\langle P(E)\rangle$ vs coupling $V$ and SOC $\alpha$: polarization increases for small $V$ and large $\alpha$. (F) Energy distribution of transmitted photoelectrons for three layer types. (A) and (D) reproduced from ref. Gohler2011 with permission. Copyright 2011, American Association for the Advancement of Science. (B), (C) and (E) reproduced from ref. Naaman2012 with permission. Copyright 2012, American Chemical Society. (F) reproduced from ref. Kaushik1999 with permission. Copyright 1999, American Association for the Advancement of Science.
• Figure 2: Schematic illustration of various mechanisms proposed as possible explanations of CISS. (A) Two representations of $G_0$ with dipoles, linking to electric polarization and current-induced magnetization. (B) Tight-binding model of a honeycomb lattice with SOC-induced chiral hopping ($\chi=-1$). Reproduced from ref. Hirakida2025 with permission. Copyright 2025, American Physical Society. (C) Examples of $\tilde{K}_{kq}$ for achiral vs. chiral phonons. (D) Spin-current tensor components vs. phonon mixing $\omega_1$. Reproduced from ref. Fransson2023 with permission. Copyright 2023, American Physical Society. (E) Schematic of spin-selective transport through a chiral molecule with SO coupling.Reproduced from ref. Dalum2019 with permission. Copyright 2019, American Chemical Society. (F) Calculated electron polarization: negligible for linear molecules, $\sim$1% for helices, reversing with handedness. Reproduced from ref. Zollner2020 with permission. Copyright 2020, American Chemical Society.
• Figure 3: Spin response and transport in coupled-helix models and dephasing regimes. (A) Band structure of the coupled-helix model and Edelstein coefficient $\chi_{zz}$ vs chemical potential and coupling $\lambda$. Reproduced from ref. Shitade2020 with permission. Copyright 2020, Institute of Physics. (B) Length dependence of spin polarization $P_s$, averaged $\langle P_s \rangle$, and conductance $\langle G^\uparrow \rangle$ with dephasing parameter $\tau_d$. Reproduced from ref. Guo2012 with permission. Copyright 2012, American Physical Society.
• Figure 4: Illustrations of spin-dependent transport and polarization in chiral and helical systems. (A) Non-equilibrium spin density isosurfaces for left- and right-handed helices under different bias voltages with Au(111) electrodes. Reproduced from ref. Sumit2023 with permission. Copyright 2023, American Chemical Society. (B) Wavefunction tail amplitude $\xi \gg 1$ grows with angular momentum, with spin aligned to velocity. Reproduced from ref. Karen2019 with permission. Copyright 2019, American Chemical Society. (C) Transport properties of achiral (gray), chiral (red), and helical (blue) structures: charge current, spin polarization, normalized polarization, and enantiomeric asymmetry under spin-polarized injection. Reproduced from ref. Fransson2025 with permission. Copyright 2025, American Chemical Society.
• Figure 5: Schematics of spin-related effects under broken $P$ and $T$ symmetries, external fields, and rotational dynamics. (A) Band deformations and spin splittings with/without inversion ($P$) and time-reversal ($T$) symmetries; arrows denote spin orientation. (B) Relations between monopoles ($Q_0,M_0,T_0,G_0$) and dipoles ($Q,M,T,G$) via external fields (E, H, J, CPL, Rot.). Reproduced from ref. Hayami2024 with permission. Copyright 2024, Physical Society of Japan. (C) Schematics of spin-dependent velocities and separation induced by SOC and helicity, leading to transient spin polarization. Reproduced from ref. Zhang2025 with permission. Copyright 2025, American Physical Society. (D) Effects of $P$, $T$, and rotation $R$ on spinning cone states. Reproduced from ref. Barron1986 with permission. Copyright 1986, American Chemical Society.