STUDY OF INTERFACE RESISTANCES IN EPITAXIAL YBA2CU3O7-X/BARRIER/YBA2CU3O7-X JUNCTIONS

We have measured interface resistances in YBa2Cu3O7-x/barrier/YBa2Cu3O7-x junctions with different barrier materials in an edge junction geometry. CaRuO3, La0.5Sr0.5CoO3, Y0.7Ca0.3Ba2Cu3O7-x, YBa2Cu2.79Co0.21O7-x, and La1.4Sro.6CuO4 have been employed as the epitaxial barrier materials. We observe interface resistances of the order of 1 X 10(-8) OMEGA cm2 when we use CaRuO3 and La0.5Sr0.5CoO3 barriers. These two barrier materials are cubic perovskites. However, in the case of the layered barrier materials, the measured interface resistances are smaller than 1 X 10(-10) OMEGA cm2. Our study suggests that the oxygen disorder at the YBa2Cu3O7-x surface, due to stress created by the thermal expansion mismatch between YBa2Cu3O7-x and the barrier, may be the origin of the interface resistances, and that the magnitude of this stress can change the resistance by orders of magnitude.