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 configurations. Firstly, the coupling of two HTS electrodes via doped manganite barriers was analyzed and secondly the interface properties between HTS and 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 was found which appears together with non-linear current–voltage characteristics. On applying external magnetic fields up to 8 T, the low temperature interface resistance is suppressed considerably. These observations can be understood 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 differential conductance spectra of YBa₂Cu₃O_7−δ–La_2/3Ca_1/3MnO₃ junctions with low transparency show a pronounced gap feature but no zero-bias conductance peak.