Imaging of Spatial Structures Of Fiske- and Shapiro-Step States and Photon-Assisted Tunneling States in Josephson Junctions
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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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