Chirality-Induced Spin Selectivity (CISS)

Chirality-induced spin selectivity refers to multiple phenomena in which the chirality of a chemical compound influences the spin of transmitted or emitted electrons. The effect is attributed to Ron Naaman and co-workers, with the landmark study being Ray, Ananthavel, Waldeck and Naaman, "Asymmetric scattering of polarized electrons by organized organic films of chiral molecules," Science 283 (5403): 814–816, February 1999.

Demonstrated manifestations

The source digest lists four experimentally demonstrated forms of the effect:

• polarization of electrons scattered from chiral molecules;
• spin-dependent transmission probabilities through layers of chiral molecules;
• spin-selectivity of electron transport in a chiral medium;
• enantio-selectivity in chemical reactions induced by spin-polarized electrons.

Theoretical status and the central caveat

Models based on spin-orbit-coupling explain CISS qualitatively, but quantitatively the predicted effect "was always orders of magnitude smaller than what was measured in experiments." The mechanism underlying CISS is explicitly described as "not completely understood." This gap between SOC-based prediction and measured magnitude is the most important unresolved question attached to the phenomenon and should be preserved in any account of it.

A hybrid method — a film of pure gold with chiral molecules on it — is reported to have produced results "on par with the magnetic method," i.e. a non-magnetic route to spin polarization comparable to conventional magnetic spin injection.

Extension to displacement currents

The Brian P. Bloom et al. review in Chem. Rev. 124, 1950 frames CISS as "the innate ability of chiral materials to act as spin filters for electron transport," and notes that more recent experiments demonstrate that displacement currents arising from charge polarization of chiral molecules lead to spin polarization without the need for net charge flow. This is a meaningful extension of the original formulation, which was framed around electron transport.

Voltage-controlled interfacial chirality

In 2025 Huang et al. reported voltage-controlled interfacial chirality on an otherwise achiral molybdenum disulfide (MoS₂ (Molybdenum Disulfide)) surface, using an electric double-layer transistor with enantiopure ionic liquids. The induced state was detected through CISS and the electrical magnetochiral effect (Science Advances 11 (47) eadx2281, doi:10.1126/sciadv.adx2281). This is notable because the chirality is induced electrically on a surface that is not intrinsically chiral.

Implications and contested framing

The Bloom review identifies a fundamental connection between chiral symmetry and electron spin in molecules and materials, with implications for existing technologies and for age-old questions such as the homochiral nature of life. The source page also links a James Tour lecture that uses CISS within an argument against a prebiotically plausible route to homochiral amino acids. That is a position/argument, not experimental evidence about CISS, and should be attributed as such.

Related pages

• Gyrotropy — the broader phenomenon of macroscopic chirality in electronic and photonic systems.
• Circular Photogalvanic Effect — a measurement technique used to detect chiral electronic order.
• Chiral Metamaterials — artificial chiral structures, largely mechanical and photonic, listed in the patent half of the source.