Synergy and Competition of Dual Chirality in the Chirality-Induced Spin Selectivity of Supramolecular Helices

Abstract

Recent progress in constructing supramolecular assemblies with hierarchical chirality offers new opportunities to investigate the chirality-induced spin selectivity (CISS) effect and its potential applications. In this work, we systematically examine the CISS effect in such multichiral systems by designing a class of multilayer helical architectures constructed of stacked and interfaced individual helical rings, each possessing well-defined local chirality. Through controlled interlayer twisting, a global helical handedness is further imposed, forming a multichiral tubular helix. Theoretical calculations reveal that these two distinct chiral hierarchies lead to several unprecedented CISS phenomena, such as enhanced spin polarization arising from cooperative dual chirality, along with the simultaneous emergence of transverse and longitudinal CISS signals. Moreover, interlayer torsional competition modulates the system's response to external fields. The dual-chiral geometry breaks the conventional symmetry of single helices, inducing an anomalous angular phase shift in magnetoresistance. Furthermore, Floquet analysis reveals that the interplay between local and global chirality enables controlled spin polarization switching under circularly polarized light. These findings provide a basic theoretical framework for studying the CISS in multichiral superstructures and establish design principles for coupled optical, magnetic, and spin manipulations, thereby facilitating the development of multichiral spintronic devices.

Figures (6)

• Figure 1: Schematic of the MCTH model and its geometric parameters. (a) (Left, Left) configuration with left-handed molecules (pink) twisted clockwise between layers, and its mirror image (Right, Right) with right-handed molecules (blue) twisted counterclockwise. (b) Mixed-chirality configurations: (Right, Left), consisting of left-handed molecules stacked with an anticlockwise (right-handed) twist, and its enantiomer (Left, Right). (c) Achiral stacking configurations: (Achiral, Left) and (Achiral, Right), where left- or right-handed molecules are stacked vertically without inter-layer twist. (d) Elementary building blocks: left-handed (pink) and right-handed (blue) circular helical molecule. (e) Magnified side view of two adjacent layers ($l$ and $l+1$) from the (Left, Left) (pink) and (Right, Right) (blue) models, showing inter-layer geometric parameters: layer spacing $h$, twist angle $\phi$, and inter-molecular space angle $\Phi_n$, illustrated using the (Right, Right) model. (f) Intra-layer geometry of a single circular helical unit in a Cartesian frame (left), and detailed local parameterization (right), where $O$ ($O'$) and $r_1$ ($r_0$) denote the center and radius of the toroidal molecule and its cross-section plane, respectively; $\varphi_n$ and $\theta_n$ are the toroidal and poloidal angles; $\Psi_n$ and $D_n$ represent the space angle and interatomic distance.
• Figure 2: Calculated CD spectra for MCTH models. (A) CD spectra of (Right, Right) and (Left, Left) configurations. (b) CD spectra of mixed-chirality (Right, Left) and (Left, Right) configurations. (c) CD spectra of achirally stacked (Achiral, Left) and (Achiral, Right) configurations. Spectra in (a-c) are calculated with SOC and fixed hopping parameters $t_{||}$=$t_{\perp}$=$100$ meV. (d) CD spectra of (Right, Right) and (Left, Left) models calculated without SOC, using the same hopping parameters. (e) Evolution of CD spectra for the (Right, Right) model (with SOC) as the inter-layer hopping ($t_{\perp}$) varies from 10 meV to 90 meV, while intra-layer hopping fixed at $t_{||} = 100$ meV. (f) Evolution of CD spectra for the (Right, Right) model (with SOC) as the intra-layer hopping ($t_{||}$) varies from 10 meV to 90 meV, while inter-layer hopping fixed at $t_{\perp} = 100$ meV.
• Figure 3: Hierarchical CISS effect in MCTH models. (a) Schematic of the two-terminal device: the MCTH is connected to a non-magnetic top electrode and a ferromagnetic bottom electrode, whose magnetization direction is set by an external magnetic field at angle $\theta_M$ relative to the helical axis. (b) Current-voltage (I-V) characteristics under opposite magnetization directions. (c) Corresponding spin polarization $P_S$ as a function of bias voltage for for different chiral configurations, calculated without electron-phonon coupling. (d) Spin-projected local density of states $\rho_{s,n}(\omega)$ for (d1) (Right, Right), (d2) (Left, Left), (d3) (Right, Left), and (d4) (Left, Right) models.
• Figure 4: Parametric modulation of the Hierarchical CISS effect in MCTHs. (a) Spin polarization as a function of the number of layers for intact and cleaved assemblies. (b) 2D map of spin polarization versus intra- and inter-layer SOC strengths. (c) 2D map of spin polarization as a function of bias voltage and top electrode contact position. (d) I-V characteristics with inset showing spin polarization, both calculated inlcuding electron-phonon coupling. (e) Temperature dependence of spin polarization for assemblies with varying numbers of layers.
• Figure 5: Magnetic control of Hierarchical CISS. (a, b) Spin polarization $P_S$ as a function of bias voltage at magnetization angles $\theta_M = 0$ and $\pi$ ($\mathcal{L}=2$) for (a) the (Left, Left) and (Right, Right) configurations and (b) the (Right, Left) and (Left, Right) configurations. (c) Angular dependence of $P_S$ on $\theta_M$ for all four chiral configurations at a fixed bias of 0.85 V. (d) Comparison of $P_S$ vs. $\theta_M$ for left-handed (red) and right-handed (blue) configurations calculated using the interlayer Ising-SOC model (solid lines with markers) and the axial single-helical model (solid lines). (e, f) Evolution of the angular dependence of $P_S$ with increasing number of layers ($\mathcal{L}$) for (e) the (Right, Right) and (f) the (Right, Left) configurations. Insets: The peak magnetization angle $\theta_M^P$ as a function of $\mathcal{L}$.