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.