First-Principles Theory of Chirality-Induced Spin Selectivity at Molecule-Metal Interfaces in Photoemission

Abstract

Spin-resolved photoelectron spectroscopy (PES) is a major experimental probe of chirality-induced spin selectivity (CISS), yet it remains unclear whether the measured spin polarization reflects molecular chirality itself or the broader electronic structure of the hybrid interface. We present a first-principles theory of PES spin polarization at chiral molecule-metal interfaces, treating the interface holistically rather than as a metal substrate plus a separate molecular spin filter/polarizer. Using density functional theory within a three-step photoemission framework, we compute the spin polarization generated in the optical-excitation step for ($M$)- and ($P$)-heptahelicene adsorbed on Au(111) and Cu(111), and for coronene/Au(111) as a non-chiral control. We find that adsorption strongly reshapes the PES spin polarization relative to the clean metal surface, but opposite enantiomers yield symmetry-related, qualitatively similar responses that are also comparable to that of the non-chiral coronene. These results indicate that changes in the PES spin polarization are more naturally attributed to the electronic structure of the hybrid interface than to molecular chirality alone.

Figures (5)

• Figure 1: Interfaces studied in this work. (a) ($M$)-[7]H, (b) ($P$)-[7]H, and (c) coronene adsorbed on Au (111). (d) ($M$)-[7]H and (e) ($P$)-[7]H adsorbed on Cu (111). The bottom metal surface is passivated with hydrogen atoms.
• Figure 2: Spin polarization along the $z$ direction. (a)(d) ($M$)-[7]H adsorbed on Au (111). (b)(e) Clean Au (111), where dashed lines are computed for a nine-layer unit cell and solid lines are computed for an Au slab with coordinates adopted from the ($M$)-[7]H/Au interface. (c)(f) ($P$)-[7]H adsorbed on Au (111). (a-c) Computed at the $\Gamma$ point. (d-f) Computed at $\mathbf{k}_\parallel=$ (0, 0.03333), expressed in fractional coordinates of the in-plane reciprocal lattice vectors. In all panels, red (blue) lines denote $\zeta^+$ ($\zeta^-$), spin polarization under right (left) circularly polarized light.
• Figure 3: Spin polarization along the $z$ direction, for coronene adsorbed on Au (111), at (a) the $\Gamma$ point and (b) $\mathbf{k}_\parallel=$ (0, 0.03333), expressed in fractional coordinates of the in-plane reciprocal lattice vectors. In both panels, red (blue) lines denote $\zeta^+$ ($\zeta^-$), spin polarization under right (left) circularly polarized light.
• Figure 4: Spin polarization along the $z$ direction. (a)(d) ($M$)-[7]H adsorbed on Cu (111). (b)(e) Clean Cu (111) slab with coordinates adopted from the ($M$)-[7]H/Cu interface. (c)(f) ($P$)-[7]H adsorbed on Cu (111). (a-c) Computed at the $\Gamma$ point. (d-f) Computed at $\mathbf{k}_\parallel=$ (0, 0.03333), expressed in fractional coordinates of the in-plane reciprocal lattice vectors. In all panels, red (blue) lines denote $\zeta^+$ ($\zeta^-$), spin polarization under right (left) circularly polarized light. This figure is analogous to Figure \ref{['fig:Au']}, but for the Cu-based systems.
• Figure 5: Electronic structure of the ($M$)-[7]H/Au interface that includes four layers of Au (111). (a) PBE band structure, with color denoting the projected character of each orbital. Fermi level of the interface is set to be zero. (b) PBE and $G_0W_0$@PBE energy level alignment at the $\Gamma$ point. Solid and dashed blue lines represent the highest occupied molecular orbital (HOMO) and the lowest unoccupied molecular orbital (LUMO) of the ($M$)-7[H], respectively. Black lines represent the Fermi level of the interface. Vacuum level is set to be zero.