Condensed Matter Seminar by Prof. Katharina Franke – Niels Bohr Institute - University of Copenhagen

Niels Bohr Institute > Calendar > 2012 > Condensed Matter Semin...

Condensed Matter Seminar by Prof. Katharina Franke

Magnetic excitations in single molecules on a superconductor 

At macroscopic length scales, magnetism and superconductivity are phenomena which are incompatible with each other: superconductors expel weak applied magnetic fields, and strong magnetic fields suppress the superconducting state. Using scanning tunnelling spectroscopy we detect the co-existence of magnetism and superconductivity and their competition in the vicinity of single magnetic molecules. 

We have deposited paramagnetic Manganese-Phthalocyanine (MnPc) molecules on top of a superconducting lead substrate. The magnetic moment of the adsorbate interacts with the Cooper pairs and tends to break them apart. Signatures of this interaction are localized states in the superconducting gap. On the other hand, the unpaired electrons in the substrate screen the localized spin via the Kondo effect. The delicate balance between these phenomena depends on the atomic scale environment of the MnPc on the Pb substrate and determines the resulting ground state of the system.
Attaching organic spacer legs to the molecules can be used to reduce the exchange coupling with the surface. In Iron-Octaethyl-Porphyrin (Fe-OEP), we detect inelastic spin flip excitations, which reveal the magnetic ground state of the molecule, while the superconducting state remains unperturbed.

Condensed Matter Seminar by Prof. Katharina Franke