物理学教室 談話会(1月27日)
コロキウム・談話会 2025/01/07
演目:Electron spin filtering and Kondo physics of helical aromatic molecules on metal surfaces
講師:Prof. Dr. Karl-Heinz Ernst1,2,3
所属:Empa, Swiss Federal Laboratories for Materials Science and Technology
日時:2025年1月27日(月)17:00-18:30
場所:理学部4号館2階1220号室
1Empa, Swiss Federal Laboratories for Materials Science and Technology, Dübendorf, Switzerland
2Nanosurf Laboratory, Institute of Physics, The Czech Academy of Sciences, Prague, Czech Republic
3Department of Chemistry, University of Zürich, 8057, Zurich, Switzerland
Soon after his seminal discovery of molecular chirality Pasteur suggested physical fields as its origin and assumed that magnetic fields must be the source of chirality in the universe. Lord Kelvin refuted Pasteur's suggestions and made clear that magnetism has no chirality. In 1894, Pierre Curie proposed that parallel and antiparallel alignments of electric and magnetic fields will induce chirality, but such chiral influence must vanish under conditions of thermodynamic equilibrium. We report that single helical aromatic hydrocarbons, so-called helicenes, undergo enantioselective adsorption on ferromagnetic cobalt surfaces. Spin- and chirality sensitive scanning tunneling microscopy (STM) reveals that molecules of opposite handedness prefer adsorption onto cobalt islands with opposite out-of-plane magnetization. As mobility ceases in the final chemisorbed state, it is concluded that enantioselection must occur in a physisorbed transient precursor state. Such observation suggests electron spin-depend van-der-Waals forces. Simultaneous measurements of the tunneling current through both enantiomers on a given Co nanoisland yields a magneto-chiral specific conductance of up to 50% for single helicene molecules, thus refuting previously proposed ensemble effects as origin of chirality-induced spin selectivity. Our results open the opportunity towards new single-molecule spin-valve devices and shine light into the origin of the so-called chirality-induced spin selectivity (CISS). Open-shell helicenes offer an exciting route to study enantioselective spin-orbit coupling in extended aromatic hydrocarbons. We present first results of single molecule Kondo scattering of such helicenes on a gold surface. The outlook for potential effects in single molecule ESR is discussed. |