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arXiv:2607.00624

Heliciton-Assisted Chirality-Induced Spin Selectivity from Helical Dirac Current

Ju Gao, Fang Shen

quant-phSubmitted Jul 1, 2026• Announced Jul 2, 2026
v1 · Jul 1, 2026v2 · Jul 17, 2026
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Abstract

We develop a quantized chiral-field mechanism for chirality-induced spin selectivity (CISS). The corresponding quantum is a heliciton: a helical mode with phase coordinate $φ-qz$, screw momentum $\hbar q$, and energy $\hbarΩ_q$. A helical electron can absorb or emit this quantum, converting the static chiral vertex developed in our preceding work into an inelastic resonant scattering process. Using first Born scattering theory, we show that an incident two-spin-channel state generates two heliciton-assisted sidebands. Absorption converts the $\uparrow k$ channel into the $\downarrow,k+q$ sideband, while emission converts the $\downarrow k$ channel into the $\uparrow,k-q$ sideband. Thus the heliciton supplies both the screw momentum and energy needed to turn the handedness-conversion into a resonant spin-selective channel. The two sidebands inherit the same sampled-current overlap $J_χ(k)$ from the static theory, but acquire different kinematic weights and different resonance detunings. The sideband sector reaches full spin polarization at the respective isolated heliciton resonances, with $P_{\rm sb}(k,q)\simeq +1$ for $Δ_-(k,q)=0$ and $P_{\rm sb}(k,q)\simeq -1$ for $Δ_+(k,q)=0$. Reversing the screw handedness, $q\rightarrow -q$, interchanges the two sideband channels and reverses the polarization. No ad hoc spin-dependent potential is introduced. The spin selectivity comes from three ingredients: helical Dirac-current texture, quantized screw-symmetric environmental motion, and resonant exchange of screw momentum and energy. This identifies CISS as a heliciton-assisted resonance mechanism that produces spin polarization in the inelastic sideband sector.

Comments
6 pages

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We develop a quantized chiral-field mechanism for chirality-induced spin selectivity (CISS). The corresponding quantum is a heliciton: a helical mode with phase coordinate φ−qzφ-qzφ−qz, screw momentum ℏq\hbar qℏq, and energy ℏΩq\hbarΩ_qℏΩq​. A helical electron can absorb or emit this quantum, converting the static chiral vertex developed in our preceding work into an inelastic resonant scattering process. Using first Born scattering theory, we show that an incident two-spin-channel state generates two heliciton-assisted sidebands. Absorption converts the ↑k\uparrow k↑k channel into the ↓,k+q\downarrow,k+q↓,k+q sideband, while emission converts the ↓k\downarrow k↓k channel into the ↑,k−q\uparrow,k-q↑,k−q sideband. Thus the heliciton supplies both the screw momentum and energy needed to turn the handedness-conversion into a resonant spin-selective channel.
The two sidebands inherit the same sampled-current overlap Jχ(k)J_χ(k)Jχ​(k) from the static theory, but acquire different kinematic weights and different resonance detunings. The sideband sector reaches full spin polarization at the respective isolated heliciton resonances, with Psb(k,q)≃+1P_{\rm sb}(k,q)\simeq +1Psb​(k,q)≃+1 for Δ−(k,q)=0Δ_-(k,q)=0Δ−​(k,q)=0 and Psb(k,q)≃−1P_{\rm sb}(k,q)\simeq -1Psb​(k,q)≃−1 for Δ+(k,q)=0Δ_+(k,q)=0Δ+​(k,q)=0. Reversing the screw handedness, q→−qq\rightarrow -qq→−q, interchanges the two sideband channels and reverses the polarization. No ad hoc spin-dependent potential is introduced. The spin selectivity comes from three ingredients: helical Dirac-current texture, quantized screw-symmetric environmental motion, and resonant exchange of screw momentum and energy. This identifies CISS as a heliciton-assisted resonance mechanism that produces spin polarization in the inelastic sideband sector.
We show that a propagating electron wave in the lowest cylindrical channel carries a spin-resolved helical conserved current, and connect this current texture to its local chiral coupling. In a weakly relativistic positive-energy Dirac projection, the two sectors have the same azimuthally symmetric charge density and opposite circulation superposed on longitudinal flow, even though their nonrelativistic orbital harmonic is l=0l=0l=0. The current is radially distributed and extends into the evanescent tail. A scalar screw potential couples these modes through a derived vertex expressed by the \emph{chiral current overlap}, Jχ\mathcal J_χJχ​. Both spatial textures determine the coupling: the environmental radial profile weights the electronic circulation, while the screw harmonic selects correlated changes of spin sector and longitudinal momentum. For a uniform static harmonic, elastic energy conservation makes the first-order spin-flip amplitude vanish within the same transverse mode. Environmental energy exchange is therefore required to activate these selected channels. The same current overlap supplies the spatial kernel for heliciton-assisted inelastic scattering in a companion study and for a subsequent transport treatment of chirality-induced spin selectivity (CISS).
We show that a propagating Dirac electron with intrinsic spin generically carries a real--space helical conserved current, even in the absence of orbital angular momentum. Using exact Dirac eigenstates in cylindrical confinement, we demonstrate that this helical structure possesses definite handedness, persists into evanescent regions, and is characterized by a geometric helix pitch independent of the longitudinal de~Broglie wavelength. This intrinsic helical geometry enables a local geometric coupling between a propagating electron and a chiral environment, yielding chirality--dependent spin selectivity through current geometry rather than through a spin--orbit coupling term.
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.
We observe and model spin currents arising from chirality and effective spin-exchange interactions in a weakly interacting ^{6}Li Fermi gas. Chirality is introduced by a static displacement between the center of the trapped atoms and the center of an applied magnetic bowl, which produces left- or right-handed spatially varying spin rotation. Spin current is directly observed via oscillations in the centers of mass of the spin-up and spin-down components, which appear to bounce off of or pass through one another, depending on the degree of handedness and s-wave scattering length. We show that this behavior obeys a driven oscillator equation with an effective spin-dependent driving force. Our measurements demonstrate chirality-induced spin selectivity via the direction of the current flow, extending CISS phenomena to Fermi gases.
We demonstrate that light propagation in reciprocal chiral photonic media admits a unified description in terms of an emergent Dirac structure in helicity space. Starting from Maxwell's equations, we reformulate the electromagnetic field as a four-component spinor governed by an effective non-Hermitian optical Dirac equation. In this representation, the magnetoelectric response of the chiral medium appears as a helicity-dependent background that modifies the spectrum and eigenmodes, while the breaking of the spin-degenerate condition generates the intrinsic spin-orbit coupling between helicity and orbital degrees of freedom. After projection onto the positive-frequency sector, the theory reduces to an exact two-level helicity-orbital model. This model is found to have an analytical solution and describes coherent Rabi-like oscillations between spin-orbit-coupled vector modes. Chirality controls the helicity splitting and detuning, whereas the electromagnetic mismatch of the medium determines the coupling strength responsible for oscillatory spin-orbit conversion. The resulting dynamics is constrained by exact conservation of the total angular momentum, leading to reversible conversion between spin and orbital angular momentum with well-defined selection rules. Our work establishes an optical Dirac framework for structured light in chiral media, and provides experimentally accessible predictions for chirality-controlled oscillations, polarization dynamics, and orbital angular momentum conversion in structured optical fields.
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.