INVESTIGATION OF YBA2CU3O7 JOSEPHSON-JUNCTIONS ON MGO BICRYSTAL SUBSTRATES

We report on the characterization of the dynamic (sc) properties of YB a2Cu3O7 Josephson junctions on MgO bicrystal substrates with 24 degree s angle. Shapiro steps have been measured in the frequency range 80-95 GHz. Measured current-voltage characteristics, as well as the depende nce of Shapiro step height on microwave power, were compared to numeri cal simulations within the RSJ model including thermal noise. At 77 K, the junctions showed ideal RSJ behavior. The occurence of half-intege r Shapiro steps at lower temperatures could be explained by an inhomog eneous critical current density of the junctions yielding a de SQUID-l ike behavior. A nonsinusoidal current-phase relation could be ruled ou t because of the periodicity of the half-integer steps.