Magnetic excitations of single atoms and molecules on superconductors probed by scanning tunneling spectroscoppy

• Applicant: Professorin Dr. Katharina Franke
• Subject Area: Experimental Condensed Matter Physics
• Term: from 2013 to 2017
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 240641355

In the framework of this proposal we will resolve the basic interaction mechanisms of atomic and molecular spins with a superconducting substrate at the atomic scale. The magnetic moment of the adsorbates couples via exchange interaction to the conduction electrons and Cooper pairs of the substrate. On the one hand, this leads to the screening of the magnetic moment via the so-called Kondo effect and, on the other hand, to a change in the pairing energy of the Cooper pairs, which is reflected in Shiba states inside the superconducting energy gap. The competition of these processes yields a complex many-body state, which we will resolve using scanning tunneling spectroscopy. In a previous work, we could experimentally demonstrate a universal correlation between the efficiency of Kondo screening and the energy of Shiba states in spin-1/2 systems, which has been predicted by theory decades ago. With these results, it also became evident that tiny differences in the atomic environment critically influence the resulting magnetic ground state. We will now increase the complexity of the spin systems and of their environment in order to integrate further factors into the picture of competing interactions. In particular, it is the goal to understand, how higher spin states of the adsorbates (S>1/2), magnetic anisotropy or exchange interactions to nearest neighbors influence the magnetic ground state and excited states. This understanding is not only of fundamental interest, but also important for realizing magnetic nanostructures for spintronic devices.

• DFG Programme: Research Grants