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    Experimentelle Physik II


    Image & Results Gallery (2020 archive)

    Tuning YSR bound states across the phase transition

    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.

    Observation of anisotropic vortices on Nb(110)

    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.