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

TL;DR

This paper develops a first-principles theoretical framework to understand spin polarization in photoemission at chiral molecule-metal interfaces, revealing that electronic structure changes, not chirality alone, dominate the observed effects.

Contribution

It introduces a holistic first-principles approach to analyze PES spin polarization at molecule-metal interfaces, challenging the notion that chirality alone causes CISS effects.

Findings

Adsorption significantly alters PES spin polarization.

Opposite enantiomers produce similar responses.

Electronic structure of the hybrid interface explains the polarization.

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.