Chirality and magnetism: Insights from surface science

Karl-Heinz Ernst^1,2*

¹IOP, Czech Academy of Sciences, Prague, Czech Republic
²Chemistry, University of Zurich, Zurich, Switzerland

* Presenter:Karl-Heinz Ernst, email:kalle@fzu.cz

Since Pasteur’s discovery of molecular chirality, the relationship between chirality and magnetism has remained a subject of debate. Pasteur proposed magnetic fields as a possible origin of chirality in nature, an idea later dismissed by Lord Kelvin. In 1894, Pierre Curie argued that coupled electric and magnetic fields could induce chirality, but only under non-equilibrium conditions. We now revisit this historical debate by showing that chirality and magnetism can indeed couple at the molecular scale in different, complementary ways.
First, we demonstrate enantioselective adsorption of single helicene molecules on ferromagnetic cobalt surfaces. Spin- and chirality-resolved scanning tunneling microscopy reveals that left- and right-handed helicenes preferentially adsorb on Co islands with opposite out-of-plane magnetization. Since mobility vanishes once molecules become immobilized in their final chemisorbed state, enantioselection must occur in a physisorbed transient precursor, suggesting spin-dependent van der Waals interactions. Concurrent tunneling conductance measurements through individual enantiomers yield magneto-chiral asymmetries of up to 50%, excluding ensemble effects as the sole origin of chirality-induced spin selectivity (CISS).
Second, we report adsorption-induced magnetism of enantiopure 7,12,17-trioxa[11]helicene (TO[11]H) monolayers on non-magnetic Cu(100). Spin-polarized low-energy electron microscopy uncovers spin-dependent reflectivity, evidencing a spin-polarized state localized in the topmost copper layer. Control experiments exclude artifacts and CISS, while spin-polarized density functional theory and an extended Newns–Anderson–Grimley model attribute the effect to strong chemisorption, where hybridization between the helicene HOMO and copper s- and d-states drives asymmetric spin-polarized charge redistribution.
Together, these studies reveal both emergent and engineered mechanisms for coupling chirality and pure adsorption to magnetism. They provide new strategies for tailoring spin-polarized states in low-dimensional organic–inorganic hybrids and pave the way toward molecular-scale spintronic functionalities.

Keywords: chirality, spin-polarised STM, magnetism, chirality-induced spin selectivity