Capacitance of Josephson junctions made on bicrystalline substrates of different geometries

The electromagnetic parameters of YBa2Cu3O7-x (YBCO) grain boundary Josephson junctions (JJs) fabricated on four different tilt bicrystal geometries: 12° [001] asymmetric, 24° [001] symmetric, 24° [001] asymmetric, and 45° [100] asymmetric, have been studied. While the Swihart velocity sc¯d is slightly affected by the nature of the barrier and mainly fixed by the junction width, a notable influence of the barrier structure, of the geometry of the bicrystal substrate, on the relative dielectric constant to the barrier thickness ratio s«/ td values has been found. Interesting barrier information can be deduced from the study of the dependence of the junction capacitance on the junction resistance. We have observed that the capacitance values deduced by means of Fiske steps in YBCO 24° [001] symmetric and 45° [100] asymmetric JJs scales with junction resistance in the opposite direction. This result could reveal the presence of a tunnel barrier in the YBCO 45° [100] asymmetric JJs. On the other hand, different capacitance values have been obtained by means of Fiske steps and hysteresis observed in the current-voltage characteristics in 45° [100] asymmetric JJs. An interpretation of this result can be made taking into account the contribution of the depleted YBCO layers close to the crystallographic grain boundary.