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arXiv:2607.06858

Explaining the magnitude of Chirality-Induced Spin Selectivity via electron-electron exchange

Bence Csakany, Alex J. W. Thom

quant-phcond-mat.mtrl-sciSubmitted Jul 7, 2026• Announced Jul 9, 2026
arXivHTMLPDF

Abstract

Chiral molecular structure can couple to electron spin, leading to unexpected spin polarization effects. This Chirality-Induced Spin Selectivity (CISS) was first reported for DNA molecules adsorbed on gold but its microscopic origin remains unclear. We demonstrated though simulation that the exchange arising from electron-electron Coulomb interactions within the self-consistent mean field (Hartree--Fock) approximation can yield significant ($\sim 2\%$) spin polarisation for $3$-methylcyclohexanone adsorbed on Cu(111) amplifying a much smaller ($\sim 0.0014\%$) initial bias, consistent with experiment. Symmetry considerations ensure the result is physically meaningful, while its ab-initio nature ensures all parameters are physically realistic. This amplification is connected to existing studies on spin-symmetry breaking in Hartree--Fock, providing a new pathway for understanding the magnitude of CISS as an emergent phenomenon of interacting electrons.

Comments
25 pages, 8 figures

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•Dec 21, 2025•0 citations
Chiral molecular structure can couple to electron spin, leading to unexpected spin polarization effects. This Chirality-Induced Spin Selectivity (CISS) was first reported for DNA molecules adsorbed on gold but its microscopic origin remains unclear. We demonstrated though simulation that the exchange arising from electron-electron Coulomb interactions within the self-consistent mean field (Hartree--Fock) approximation can yield significant (∼2%\sim 2\%∼2%) spin polarisation for 333-methylcyclohexanone adsorbed on Cu(111) amplifying a much smaller (∼0.0014%\sim 0.0014\%∼0.0014%) initial bias, consistent with experiment. Symmetry considerations ensure the result is physically meaningful, while its ab-initio nature ensures all parameters are physically realistic. This amplification is connected to existing studies on spin-symmetry breaking in Hartree--Fock, providing a new pathway for understanding the magnitude of CISS as an emergent phenomenon of interacting electrons.
The chirality-induced spin selectivity (CISS) effect, the coupling between structural chirality and electron spin polarization, has been experimentally observed across many diverse systems. However, despite extensive theoretical effort, a unified mechanistic understanding remains elusive. In this perspective, we demonstrate how some of the basic properties of the fascinating effects of CISS can be understood based on straightforward symmetry considerations commonly employed in fundamental particle physics. In particular, we show that CISS does not violate any fundamental symmetries including parity and time-reversal. By anchoring CISS within the universal language of symmetry, we offer a robust conceptual foundation for interpreting experiments and guiding future theoretical and experimental designs.
The chirality-induced spin selectivity (CISS) effect has been invoked to explain recent reports of differences in the time-resolved EPR signals between chiral and achiral molecules. However, the microscopic origin of these differences and their connection to CISS remains contested, particularly since these systems lack a metal interface. Here we introduce an intramolecular spinterface-like mechanism that naturally arises within donor-chiral bridge-acceptor (D--χχχB--A) complexes and quantitatively reproduces experimentally reported observed spin polarization in time-resolved EPR studies. In our two-electron Lindblad model, the photoexcited charge-transfer electron traversing the chiral bridge exchanges with the residual donor electron, which acts as a localized magnetic moment analogous to an induced magnetic moment on an electrode surface. The resulting through-bridge charge current produces an effective solenoidal field at the donor--bridge interface, breaking spin degeneracy and directional symmetry, thus enabling spin-selective transport without invoking intrinsic spin-orbit coupling on the bridge. We show that the interplay between this current-induced field, donor thermalization (which breaks time-reversal symmetry), and bridge spin mixing yields tens-of-percent polarization over realistic experimental conditions and charge-transfer time scales, matching reported CISS signatures in triads and DNA hairpins. By explicitly resolving the dependence on solenoidal coupling strength, temperature, and spin-mixing rates, the model identifies the regime in which internal spinterfaces can generate robust CISS-like spin filtering. These findings demonstrate that CISS-like signals in isolated D--χχχB--A complexes are fully compatible with a spinterface mechanism, providing a unified conceptual framework for interpreting both device-based and molecule-internal CISS platforms.
Whether chirality-induced spin selectivity (CISS) reflects coherent SU(2) spin rotation or incoherent spin-dependent filtering is a central unresolved question in molecular spintronics, with implications ranging from asymmetric chemistry to quantum information. We show that these two scenarios are distinguishable by a sharp symmetry criterion on the superexchange interaction mediated by a chiral molecular bridge. Coherent CISS, implemented as a unitary spin rotation of the tunneling electron, generates a giant Dzyaloshinskii-Moriya (DM) interaction with ratio |D|/JH up to 3, which is two orders of magnitude beyond intrinsic Rashba spin-orbit coupling in Si/SiGe. Incoherent CISS, represented by any Hermitian (non-unitary but spin-diagonal) tunneling matrix, produces D = 0 identically; we prove this as a structural theorem, reinforced by a Lindblad argument that dissipative spin filtering cannot modify virtual-tunneling-mediated superexchange. The DM interaction thus serves as a coherence order parameter, nonzero only when quantum amplitudes for opposite-spin transmission maintain a fixed relative phase. We derive closed-form angular, enantiomeric, and sensitivity signatures and show that the critical coherent rotation angle lies two orders of magnitude below current transport-inferred values and is accessible to existing 10 kHz exchange spectroscopy in gate-defined quantum dots. Five candidate molecules are predicted to exceed this threshold by one to two orders of magnitude even in a conservative interface-amplification scenario. The proposed measurement converts a long-standing transport controversy into a binary spin-qubit experiment with quantum-amplitude resolution.
Chiral-induced spin selectivity (CISS) enables spin selectivity of charge carriers in chiral molecular systems without magnetic materials. While spin selectivity has been widely investigated, its quantum coherence has not yet been explored. Here, we investigate spin-dependent photoluminescence (PL) dynamics in multilayer quantum-dot (QD) assemblies coupled by chiral linkers. Using circularly polarized excitation in the presence of an external magnetic field, we observe a pronounced modulation of the PL lifetime that depends on the magnetic field magnitude and geometry. The lifetime difference between left- and right-circularly polarized excitations exhibits a field-angle dependence, consistent with spin precession driven by the transverse magnetic-field component relative to the chiral axis. A model incorporating coupled spin precession and decay processes reproduces the experimental trends. These results establish chiral QD assemblies as a room-temperature platform for probing quantum coherent manifestations of the CISS effect, with implications for spintronic and quantum technologies.
Molecular chirality plays a crucial role in physics, chemistry, life sciences and pharmacology. Nowadays, the chiral discrimination and control at the single-molecule level is urgently needed to reveal the origin of the chirality-relevant phenomena by recovering the information disturbed by the ensemble averaging. The method of magnetic resonance (MR), as one of powerful tools for structure analysis, is blind to the molecular chirality in the absence of a chiral reagent. Here we propose and experimentally demonstrate a direct MR-based method for determining the chirality at the single-molecule level through constructing the symmetry-breaking dynamics of nearby nuclear spins. In principle, the mirror asymmetry of two enantiomers in real space is manifested by breaking the joint symmetry of the mirror reflection and time reversal in spin space under spin dynamics. Experimentally, two enantiomers are indistinguishable from the dynamics of strongly-coupled but unpolarized nuclear spins, but diverge evidently in the dynamical results that break the field-inversion symmetry after spins are polarized. Our method and results will benefit the study of chirality-induced properties in the fields of chemistry and biology.
The Chiral-Induced Spin Selectivity (CISS) effect—where electrons are filtered by their spin when passing through chiral molecules—presents a major puzzle in quantum biology. Conventional theories often rely on assumed strong internal electric fields. We propose a radical alternative based on Superfluid Vacuum Topological-Geometric Dynamics (SV-TGD): CISS is a macroscopic hydrodynamic sieving process. In this view, an electron is a microscopic vortex carrying circulation, and a chiral molecule acts as a "rifled barrel" that imposes a helical vortex field on the vacuum fluid. Spin-matched electrons flow smoothly; spin-mismatched ones are deflected by a transverse Magnus force. This purely mechanical picture yields testable predictions and stems from a deeper identity: the Lorentz force is mathematically equivalent to the Magnus force in a fluid vacuum.