Regensburg 2013 – wissenschaftliches Programm
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TT: Fachverband Tiefe Temperaturen
TT 12: Poster Session Superconductivity
TT 12.35: Poster
Montag, 11. März 2013, 15:00–19:00, Poster D
Josephson currents and resonances observed in STM experiments at milli-Kelvin temperatures — •Berthold Jäck1, Matthias Eltschka1, Maximilian Assig1, Markus Etzkorn1, Christian R. Ast1, and Klaus Kern1,2 — 1Max-Planck Institute for Solid State Research, D-70569 Stuttgart — 2Ecole Polytechnique Fédérale de Lausanne, CH-1015 Lausanne
Superconducting tunnel junctions allow for the detailed investigation of various tunneling regimes. Besides the superconducting quasi-particle tunneling, new tunneling paths such as the Josephson effect and Andreev reflections open up as the tunneling barrier is decreased. These processes manifest themselves as new structures within the gap of the superconducting quasi-particle density of states. We investigated these sub-gap structures in a Vanadium-Vanadium tunnel junction by using a Scanning Tunneling Microscope (STM) operating at 15 mK. One of the main advantages of using an STM setup is the very precise control of the tunneling resistance and hence the superconductor’s coupling, which is a central property of the tunneling processes. We observe harmonic sub-gap features at energies of about 100 µ eV which do not originate from Andreev reflections. Their peak positions neither depend on the superconductor’s coupling nor on magnetic fields, but change for different Vanadium tips. We will discuss these experimental findings in the framework of low-impedance tunneling junctions and Josephson junctions coupled to an electro-magnetic environment.