Imaging of Spatial Structures Of Fiske- and Shapiro-Step States and Photon-Assisted Tunneling States in Josephson Junctions
We report the first experimental results obtained by Low Temperature Scanning Electron Microscopy (LTSEM) on dynamic states of Josephson tunnel junctions. The spatially resolved measurements dealing with self-resonant modes (Fiskesteps) revealed information about the distribution of the rf-magnetic field amplitudes inside the Josephson junction. We imaged one- and two-dimensional cavity-modes inside a square junction. By coupling a Josephson element phase-coherently to a microwave field we imaged the distribution of the maximum current density of the generated constant-voltage steps (Shapiro-steps). For junction designs used as modern voltage standards we measured homogeneously distributed step-current densities up to the fourth step. By irradiating superconducting tunnel junctions with microwaves photon-assisted tunneling of quasiparticles takes place. Using LTSEM we imaged the standing microwave pattern inside the junction. As a result, the wavelength of the microwave inside a single tunnel junction and the wavelength inside a superconducting stripline is displayed directly. The spatial resolution achieved by LTSEM is about 1–2 μm.
KeywordsJosephson Junction Tunnel Junction Tunneling Conductivity Josephson Current Superconducting Tunnel Junction
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