Capacitive properties of YBa/sub 2/Cu/sub 3/O/sub 7/ grain boundary Josephson junctions fabricated on 45/spl deg/ [100] tilt asymmetric and 24/spl deg/ [001] tilt symmetric bicrystals

摘要

We present a comparative study of the electromagnetic parameters, mainly focused in the analysis of the capacitance (C) associated to the barrier, of YBa/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) grain boundary Josephson junctions (GBJJs) fabricated on 24/spl deg/ [001] symmetric and 45/spl deg/ [100] asymmetric tilt bicrystalline substrates. The Swihart velocity (c~) 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 (/spl epsiv//sub 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/spl deg/ [001] symmetric and 45/spl deg/ [100] asymmetric GBJJs scale with junction resistance in opposite direction. This result could reveal the presence of a tunnel barrier in the YBCO 45/spl deg/ [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/spl deg/ [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.