Speaker: Prof. Dr. Karl-Heinz Ernst (Empa, Swiss Federal Laboratories for Materials Science and Technology, Switzerland)

 

Time: 3:30 PM, January 12 (Monday), 2026

 

 

Contact: Dr. Cheng-Tien Chiang 江正天博士

 

Abstract: Soon after his seminal discovery of molecular chirality, Pasteur suggested that physical fields might underlie its origin and proposed magnetism as a source of chirality in the universe. Lord Kelvin later refuted this idea, demonstrating that magnetism itself is achiral. In 1894, Pierre Curie proposed that chirality could arise from parallel or antiparallel alignments of electric and magnetic fields, although such effects should vanish under thermodynamic equilibrium. Here, we demonstrate that single helical aromatic hydrocarbons (helicenes) undergo enantioselective adsorption on ferromagnetic cobalt surfaces. Spin- and chirality-sensitive scanning tunneling microscopy (STM) reveals that helicenes of opposite handedness preferentially adsorb on cobalt nanoislands with opposite out-of-plane magnetization [1]. Since molecular mobility ceases in the final chemisorbed state, enantioselection must occur in a transient physisorbed precursor state, suggesting the presence of spin-dependent van der Waals interactions.

 

Simultaneous tunneling-current measurements through individual enantiomers on the same Co nanoisland yield a magneto-chiral conductance asymmetry of up to 50% for single helicene molecules. This observation rules out previously proposed ensemble-based mechanisms for chirality-induced spin selectivity (CISS) and establishes CISS as an intrinsic single-molecule effect [2]. These findings open pathways toward single-molecule spin-valve devices and provide fundamental insight into the microscopic origin of CISS. In addition, we report aperiodic chiral tiling formed by more flexible helicene derivatives, representing an unprecedented two-dimensional transmission of molecular chirality into mesoscopic structures via topological assembly strategies [3].

 

Finally, we demonstrate adsorption-induced magnetism in enantiopure trioxa[11]helicene (TO[11]H) monolayers on non-magnetic Cu(100). Spin-polarized low-energy electron microscopy (SP-LEEM) reveals spin-dependent electron reflectivity, indicating the formation of a spin-polarized state localized in the topmost copper layer. Control experiments exclude artifacts and CISS-related effects. Spin-polarized density functional theory calculations, together with an extended Newns–Anderson–Grimley model, attribute the phenomenon to strong chemisorption: hybridization between the helicene HOMO and copper s- and d-states induces asymmetric, spin-polarized charge redistribution at the interface [4]. All these phenomena establish molecular chirality as an active control parameter for spindependent surface interactions, opening new routes toward chiral spintronics and singlemolecule devices.

[1] M. R. Safari, F. Matthes, V. Caciuc, N. Atodiresei, C. M. Schneider, K.-H. Ernst, D. Bürgler, Advanced Materials 36, 202308666/1–8 (2024)
[2] M. R. Safari, F. Matthes, C. M. Schneider, K.-H. Ernst, D. Bürgler, Small 19, 2308233/1–7 (2024)
[3] J. Voigt, K. Martin, M. Baljozović, C. Wäckerlin, N. Avarvari, K.-H. Ernst, Nat. Commun. 16, 83/1–9 (2025)
[4] M. M. Baljozović, S. Karmakar, A. L. Fernandes Cauduro, M. Shyam Sundar, M. Lozano, M. Kumar, D. Soler Polo, A. K. Schmid, A. V. Bedekar, P. Jelinek, K.-H. Ernst, https://arxiv.org/pdf/2510.03897