November 13, 2020
Introducing magnetic impurities onto a clean metal surface gives rise to the Kondo effect. If the substrate is superconducting, the impurities additionally create a pair-breaking potential for Cooper pairs, resulting in the so-called Yu-Shiba-Rusinov bound states. In a joint project with the group of Prof. Giorgio Sangiovanni we demonstrated that the YSR states of single Fe atoms on Nb(110) are strongly effected by the adsorbtion site of the atoms and the presence of oxygen on the surface. Oxygen increases the coupling of the impurity spin to the conduction electrons, leading to strong Kondo screening and a quantum phase transition of the YSR bound states. The result has been published in Phys. Rev. B.
November 6, 2020
Magnetic vortices in superconductors have gained a renewed interest in the recent past, as they host Majorana bound states, if the superconductivity is topologically non-trivial. However, the presence of additional trivial bound states inside vortex cores demands for an careful investigation of the bound states' energies and spatial extend to identify potential topological modes. We demonstrated that the (110) surface of the s-wave superconductor Nb exhibits strongly anisotropic vortices and an unusual distance-dependend energy splitting of the associated bound states. Together with theoretical calculations performed by the research groups of Prof. Stefan Heinze (Kiel) and Prof. Björn Trauzettel we were able to link our observations to the strongly anisotropic Fermi surface of Nb(110). The result has been published in Phys. Rev. B.