Special seminar - Berthold Jäck, Max-Planck Institute, Stuttgardt, "The Josephson effect as a local probe for superconductivity"

Fri, Oct 23, 2015, 1:00 pm to 2:00 pm
Location: 
Jadwin 111
Berthold Jäck, Matthias Eltschka, Markus Etzkorn, Christian R. Ast, and Klaus Kern In Josephson junctions the Josephson critical current I0 directly relates to the superconducting order parameter Δ [1]. Hence, the combination of the Josephson effect and Scanning Tunneling Microscopy (JSTM) has high potential as a local probe for superconductor physics, addressing questions such as the interaction of a superconducting ground state with magnetic moments at the atomic scale, a topic that recently gained significant attraction due to the experimental observation of Majorana fermions [2–4]. Extracting experimental values of I0 from STM experiments is, however, challenging since the small capacitance of the STM junction strongly affects the junction properties, making it very sensitive to its environment. Using P(E)-theory we can model the inelastic energy exchange of our tunnel junction with its electromagnetic environment [5–8]. We show that the Josephson coupling energy, experimentally determined in this regime with P(E)-theory, directly corresponds to the critical current I0 as calculated from the Ambegaokar-Baratoff formula [1]. In this way, we can determine local values of the Josephson critical current with high precision. Furthermore, we experimentally determine the range of validity for P(E)-theory, which is in accordance with theoretical predictions. In this way, we establish an optimal parameter range, in which Josephson STM can be performed [9]. [1] Ambegaokar, V. and Baratoff, A. Phys. Rev. Lett. 10, 486–489 (1963). [2] Yazdani, A., Jones, B. A., Lutz, C. P., Crommie, M. F., and Eigler, D. M. Science 275, 1767 (1997). [3] Flatté, M. H., Byers, J. M. Phys. Rev. Lett. 78, 19 (1997). [4] Nadj-Perge, S., Drozdov, I. K., Li, J., Chen, H., Jeon, S., Seo, J., MacDonald, A. H., Bernevig, B. A., and Yazdani, A. Science 346, 602 (2014). [5] Devoret, M., et al. Phys. Rev. Lett. 64, 1824 (1990). [6] Averin, D., Nazarov, Y., and Odintsov, .A. Physica B: Condensed Matter 165-166, 945 (1990). [7] Ingold, G.-L., and Grabert, H. Europhys. Lett. 14, 371 (1991). [8] Jäck, B., Eltschka, M., Assig, M., Hardock, A., Etzkorn, M., Ast, C. R., and Kern, K. Appl. Phys. Lett. 106, 013109 (2015). [9] Jäck, B., Eltschka, M., Assig, M., Hardock, A., Etzkorn, M., Ast, C. R., and Kern, K. submitted (2015).