Capacitive Properties of YBa2Cu3O7-x grain boundary Josephson junctions fabricated on 45° [100] tilt asymmetric and 24° [001] tilt symmetric bicr

We present a comparative study of the electromagnetic
parameters, mainly focused in the analysis of the capacitance
(C) associated to the barrier, of YBa2Cu3O7 x (YBCO) grain
boundary Josephson junctions (GBJJs) fabricated on 24 [001]
symmetric and 45 [100] asymmetric tilt bicrystalline substrates.
The Swihart velocity ( ) is slightly affected by the nature of the
barrier and mainly fixed by the junction width. However, a notable
influence of the barrier structure, so of the geometry of the
bicrystal substrate, on the relative dielectric constant to the barrier
thickness ratio ( r t) values, so on C, has been found. We have
observed that the capacitance values deduced by means of Fiske
steps in YBCO 24 [001] symmetric and 45 [100] asymmetric
GBJJs scale with junction resistance in opposite direction. This result
could reveal the presence of a tunnel barrier in the YBCO 45
[100] asymmetric GBJJs. 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
GBJJs. An interpretation of this result can be made taking
into account the contribution of the depleted YBCO layers close to
the crystallographic grain boundary.