Chiral molecular films as electron polarizers and polarization modulators

TL;DR

This paper demonstrates that chiral molecular films, especially self-assembled monolayers of helical molecules, can efficiently polarize electrons through multiple scattering and spin-orbit interactions, even without heavy nuclei.

Contribution

It explicitly models electron scattering off chiral molecules and predicts polarization effects, including energy windows and amplification mechanisms, aligning with recent experimental findings.

Findings

Double scattering is necessary for longitudinal polarization.

Energy-dependent polarization windows are predicted.

Polarization increases linearly with helix turns, matching experiments.

Abstract

Recent experiments on electron scattering through molecular films have shown that chiral molecules can be efficient sources of polarized electrons even in the absence of heavy nuclei as source of a strong spin-orbit interaction. We show that self-assembled monolayers (SAMs) of chiral molecules are strong electron polarizers due to the high density effect of the monolayers and explicitly compute the scattering amplitude off a helical molecular model of carbon atoms. Longitudinal polarization is shown to be the signature of chiral scattering. For elastic scattering, we find that at least double scattering events must take place for longitudinal polarization to arise. We predict energy windows for strong polarization, determined by the energy dependences of spin-orbit strength and multiple scattering probability. An incoherent mechanism for polarization amplification is proposed, that increases the polarization linearly with the number of helix turns, consistent with recent experiments on DNA SAMs.