GENERAL PHYSICS COLLOQUIUM _____ Title: Competition of magnetism and superconductivity at the nanoscale Speaker: Katharina Franke, Freie Universität Berlin Time: Wednesday, 14 September, 2011 at 3:15 p.m. Place: Physics Auditorium, 3rd floor, Department of Physics Abstract Magnetism and superconductivity are often thought to be incompatible with each other. Superconductors expel weak applied magnetic fields, and they lose their ability to carry electric current without resistance in strong magnetic fields. Using scanning tunnelling microscopy we detect the co-existence of magnetism and superconductivity and their competition at the level of single atoms. We have deposited magnetic molecules on top of a superconducting lead substrate. The magnetic moment of the adsorbate then interacts with the Cooper pairs and tends to break them apart. On the other hand, the normal electrons also present in the substrate can screen the localized spin via the Kondo effect. The delicate balance between these phenomena determines the resulting ground state of the system, i.e. whether a small magnetic moment is locally retained or compensated and whether the superconducting state still persists. The interaction strengths of Kondo screening and pair breaking largely depends on the adsorption configuration. Magnetic molecules arranged in a Moire lattice on the surface thus give rise to a magnetic pattern in which the different ground states co-exist. _____ Coffee/tea and cake will be served at 3 p.m. David Field