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.

Electrostatic alternative to the spin-transport interpretation

A 2024 preprint by Tirion and van Wees (University of Groningen) argues that the large two-terminal magnetoresistance reported in CISS experiments does not require spin-dependent transport. Their Electrostatic Contact-Potential Mechanism for CISS Magnetoresistance proposes that a chirality-dependent electrostatic contact potential at the molecule–ferromagnet interface, observed experimentally to shift by roughly 50 mV on magnetisation reversal, modifies the Schottky-like transport barrier in equilibrium and thereby generates magnetoresistance in linear response. This mechanism would also explain the apparent failure of the Onsager reciprocity relations — a central unresolved problem in the CISS field — since the system's equilibrium state itself depends on magnetisation direction.

First direct spatial imaging of spin distribution

Lee, Namgung and colleagues at UNIST report the first real-space visualisation of current-induced spin polarisation in a CISS device, using reflective magnetic circular dichroism on chiral tellurium nanowires with graphene electrodes (Real-Space Imaging of Spin Polarisation in CISS Devices). The spin polarisation in the nanowire and in both electrodes shares the same sign — a result the authors describe as strongly indicative of a "spin polariser" mechanism rather than the spin-filter picture. The observation that spin polarisation reverses with chirality and with current direction, scales linearly with current amplitude, and relaxes over several micrometres into the graphene is consistent with the interplay of chirality and intrinsic spin-orbit coupling driving the effect.

The spinterface model as a candidate unified theory

A 2025 critical perspective by Sarkar, Sharoni, Monti and Dubi (The Spinterface Mechanism for CISS: A Critical Perspective) evaluates the "spinterface model," which attributes the CISS effect to the stabilisation of fluctuating magnetic moments at the electrode surface by a feedback loop between electron motion in the chiral molecule and exchange or spin-orbit interactions at the interface. The authors argue that this is the only CISS theory to have quantitatively reproduced raw experimental current–voltage data across multiple systems, and they list falsifiable predictions and unresolved weaknesses including the unknown microscopic origin of the surface moments.

Community theory baseline

A 22-author review led by Evers and Kronik (arXiv, August 2021) sets out the state of CISS theory across the transmission, transport and chemical-reaction categories (Theory of CISS: Progress and Challenges (Evers, Kronik et al., 2021)). It concludes that SOC-based calculations still fall short of measured magnitudes and that gauge and Onsager symmetry constraints limit what any two-terminal model can predict.

Reservoir-induced spin locking as an answer to Onsager

A 2025 preprint by Jonas Fransson (Uppsala University) argues in a model calculation that a chiral molecule coupled to an electron reservoir locks into a chirality-determined spin configuration. In that model the molecule's charge depends linearly on the electrode's magnetisation, so no linear-response regime exists and Onsager reciprocity would not apply (Reservoir-Locked Spin Configurations and the Onsager Objection to CISS (Fransson, 2025)). The paper contains no new measurements or quantitative fits.