Conductance-voltage characteristics of interfaces between YBa2Cu3O7 and metallic oxides

We present the conductance-voltage characteristics of interfaces between YBa2Cu3O7 and three conductive metallic oxides; CaRuO3, SrRuO3, and La0.5Sr0.5CoO3. In the case of all the YBa2Cu3O7/(Ca,Sr)RuO3 interfaces, we observe the zero bias conductance peaks with the increasing conductance background at high bias. The zero bias conductance peaks decrease with increasing temperature and disappear at temperatures between 30 and 40 K. However, we did not observe zero bias anomalies in the YBCO/La0.5Sr0.5CoO3 contacts, in spite of an interface resistance of similar magnitude. This work suggests that the origin of the zero bias conductance peak lies in the defects on the YBCO surface and the exact defect structure depends on the adjacent epitaxial material. (C) 1996 American Institute of Physics.