Interface Conduction between Conductive ReO 3 Thin Film and NdBa 2 Cu 3 O 6 Thin Film
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Interface Conduction between Conductive ReO3 Thin Film and NdBa2Cu3O6 Thin Film Manabu Ohkubo, Kumiko Fukai, Kohji Matsuo, Nobuyuki Iwata and Hiroshi Yamamoto Department of Electronics & Computer Science, College of Science & Technology, Nihon University 7-24-1 Narashinodai, Funabashi-shi, Chiba 274-8501, Japan ABSTRACT The Re oxide films were deposited on quartz glasses by RF reactive sputtering from a Re metal target. The lowest resistivity was observed in the film in-situ annealed at 200˚C in Ar atmosphere and showed the order of 10-4 cm of which the value was still about 10 times as large as that of a single crystal ReO3. The temperature dependence of the resistivity revealed a metallic behavior. A superconductivity did not take place in the bilayered film of ReO3 / NdBa2Cu3O6. In the interface region the resistivity minimum probably caused by the Kondo effect was observed in the neighborhood of 120K.
INTRODUCTION Most high-Tc cuprates superconductors have two-dimensional multilayered structures with CuO2 planes. The cuprates show superconductivity when enough carriers are doped to the CuO2 planes from a charge reservoir block (CRB). We have been interested in rhenium (Re) oxides  as the candidate of a CRB because multi-valences, +2 ~ +7, of Re ions are noticeable in various Re oxides. We propose the multilayered films with ReO3 (CRB) and cuprates superconductors in order to synthesize novel high-Tc superconductors. Especially an infinite layered cuprates is expected to become the candidate of the pair material for Re oxides. It is well known that the ReO3 reveals extremely high conductivity comparable to that of Ag. The structure of ReO3 is simple as shown in Figure 1. It was, however, difficult to obtain Re oxide films due to vigorous sublimation at comparatively low temperature. The purposes of this work are to prepare the Re oxide thin films and to study the resistivity of the ReO3 thin film, and to evaluate it as the material of a CRB. As a preliminary research we
Figure 1. The structure of ReO3.
have carried out the deposition of ReO3 thin films on reduced nonsuperconductive NdBa2Cu3O6 films, and discussed the transport properties of the bilayered films. EXPERIMENTAL We prepared the rhenium oxide thin films by reactive RF sputtering from the target which was compressed Re powder or a metal Re disk. The substrates were quartz glasses. The distribution of temperature on the substrate was kept constant and uniform by using a copper sheet between the substrate and its holder. The RF electric power was about 100 W. The reactive and sputtering gases were O2 and Ar, respectively. The pressure of the gas was Ar / O2 = 90 / 10 mTorr. The substrate temperature was changed from ambient to 240˚C. In the case of ambient substrate, the prepared films were in- situ annealed in the temperature range from 150˚C to 300˚C for 30 minutes after the film deposition. Superconductive NdBa2Cu3O7 films were prepared by a pulsed Laser ablation deposition. The detailed preparation conditions will appe