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© The American Physical Society. The authors would like to thank C.A.I de Implantación Iónica from the Universidad Complutense in Madrid for assistance with lithography facilities. Financial support from CICYT Grant No. BMF2001-1419 is acknowledged. This work has been partially supported by the ESF Network “Pishift,” the project DG236RIC “NDA,” the TRN “De-QUACS,” and the regional project L.R. N.5 “Proprietà di trasporto e di interfaccia in giunzioni Josephson HTcsu scala submicrometrica.”, The electromagnetic parameters of YBa2Cu3O7-x (YBCO) grain boundary Josephson junctions (JJs) fabricated on four different tilt bicrystal geometries: 12degrees [001] asymmetric, 24degrees [001] symmetric, 24degrees [001] asymmetric, and 45degrees [100] asymmetric, have been studied. While the Swihart velocity ((c) over bar) 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 (epsilon/t) 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 24degrees [001] symmetric and 45degrees [100] asymmetric JJs scales with junction resistance in the opposite direction. This result could reveal the presence of a tunnel barrier in the YBCO 45degrees [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 45degrees [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., CICYT, ESF Network “Pishift”, Depto. de Estructura de la Materia, Física Térmica y Electrónica, Depto. de Óptica, Fac. de Ciencias Físicas, TRUE, pub

Analysis of the in-plane resistivity of a Tl2Ba2CaCu2O8+delta thin film and of several oxygen-deficient YBa2Cu3O7-delta single crystals in magnetic fields 0less than or equal toBless than or equal to12 T applied along the crystallographic c axis were performed to study the resistive transition into the glassy state. The transition curves were scaled according to a modified model for the vortex-liquid resistivity, finding good scaling only for fields below a certain value B-0, consistent with the field-induced crossover between a three-dimensional and quasi-two-dimensional regime of the vortex fluctuations reported in several works. This indicates that for low fields the vortex state is in fact three dimensional and provides further support to a coherent description of the vortex-liquid resisitivity., QC 20110125