FIELD-DEPENDENCE OF THE JOSEPHSON CURRENT AND FISKE RESONANCES IN SPECIALLY SHAPED JOSEPHSON-JUNCTIONS

We investigated the magnetic-field dependence of the Josephson current and Fiske resonances in specially shaped Josephson junctions. In orde r to be able to use junctions for high-resolution X-ray spectroscopy, a very good suppression of the sidelobes of both the Josephson current and the Fiske resonances must be achieved. In a theoretical argument we show that a properly chosen junction shape leads to the sidelobe su ppression of both the critical current and Fiske resonance amplitudes. The Josephson current and Fiske resonance amplitudes were measured as a function of the magnetic field, for junctions fabricated in Nb/Al t echnology. As expected, a very good sidelobe suppression was obtained for quartic-shaped junctions. For junctions with anodized structures w ithin the tunneling area, the shape of the internal structures is refl ected in the field dependence of both the Josephson current and the Fi ske resonances. Finally, Fiske modes in these junctions have been imag ed with low-temperature scanning electron microscopy, and we conclude that a quartic junction can be approximated by a rectangle, to describ e the lower-order Fiske modes, whereas the high-order modes are specif ic to the exact shape of the junction.