Condensed-Matter Physics & Materials Science Seminar

The proximity and Josephson effects are well-known phenomenon and widely used terms in superconductivity. Due to the recent advances in fabrication techniques those phenomenon has been extensively studied to give a new insight to the superconductor-based device applications. Nevertheless, many of these works addressed macroscopic properties of the samples, and thus local information is still missing. In this talk, I will discuss how we can realize the proximity effect and Josephson effect using scanning tunneling microscope at a nanometer scale. In the first part of the talk, we address how the local surface structure can influence on the proximity effect at the interface between superconducting two-dimensional Pb islands and a single-atomic-layer metal by performing local tunneling spectroscopy. From the spectroscopic mapping taken around the Pb-based S/N interface, we observed the gap at the Fermi energy, reminiscent of the superconducting gap, propagating into the metal region (proximity effect) and its depth decaying with the distance from the interface. Additionally, we observed that the propagation of the gap is terminated by the steps of the substrate and enhancement of the gap-depth in the area between the interface and the step edge. The experimental results are compared with the results of quasi-classical theory based on the Usadel equation. [1] The second part of the talk addresses atomic-scale S-S junctions by using scanning tunneling microscopy and spectroscopy. In our local conductance measurements between superconducting Pb islands on Si(111) or Ge(111) and Pb layers on the end of PtIr tip apex, we observed evolution of not only the normal-state conductance [2] but also a zero-bias peak (ZBP) from tunnel to atomic contact, which corresponds to the Josephson current, with a decrease in the tip-substrate distance on the different atomic sites on the surface crystalline lattice of the substrate. With a help of multiple Andreev reflectio