Heteroepitaxial growth of high-temperature superconductors and doped manganites in ramp type geometry

We have studied heteroepitaxially grown ramp type structures consisting of high-temperature superconductors (HTS) and doped manganites in various conf igurations. Firstly, the coupling of two HTS electrodes via doped manganite barriers was analyzed and secondly the interface properties between HTS an d doped manganites as well as between doped manganites with different Curie temperatures have been investigated. As a common feature of the interfaces involving doped manganites an increase in resistance at low temperatures w as found which appears together with non-linear current-voltage characteris tics. On applying external magnetic fields up to 8 T, the low temperature i nterface resistance is suppressed considerably. These observations can be u nderstood in terms of a spin glass behavior of the doped manganites just at the interface caused by strain due to lattice misfit and disorder. The dif ferential conductance spectra of YBa2Cu3O7-delta-La2/3Ca1/3MnO3 junctions w ith low transparency show a pronounced gap feature but no zero-bias conduct ance peak. (C) 2001 Elsevier Science B.V. All rights reserved.