A quasi-two-dimensional electron system resulting from a layered crystal structure is a common feature of high-temperature superconductors. In such a system, an interlayer Josephson coupling is responsible for bulk superconductivity. However, materials of interest are limited for Bi-based cuprates which have underdamped and systematically controllable interlayer Josephson junctions. Here, we report the c-axis transport properties and an interlayer Josephson coupling of a 1212-type cuprate superconductor which have not been well studied so far. We demonstrate an underdamped Josephson coupling between superconducting CuO2 double-layers through a chemically controllable (Pb,Cu)–O barrier layer. Broadly tunable Josephson properties through a chemical substitution demonstrated in this work in conjunction with a rich variety of barrier layers for 1212-type cuprates can potentially offer a material breakthrough in the research field of intrinsic Josephson junctions.
後藤准教授が筆頭著者の真空電子デバイスに関する論文がIEEEの雑誌、IEEE Transactions on Electron Devicesに掲載されました。
Y. Gotoh et al., “Development of a Field Emission Image Sensor
Tolerant to Gamma-Ray Irradiation”,
IEEE Transactions on Electron Devices Volume 67, Issue 4,
pp. 1660-1665 (2020). https://doi.org/10.1109/TED.2020.2977674
LuFe2O4 has been the most extensively studied among a series of RFe2O4 (R = Sc, Y, In and Dy to Lu) compounds, which possess both dielectric and magnetic orderings originating in equal numbers of Fe2+ and Fe3+ ions in a triangular lattice. We have prepared LuFe2O4 thin films epitaxially grown on a (111)-oriented YSZ (yttria-stabilized zirconia) substrate via a pulsed laser deposition method and found that the resultant thin film comprises a curious self-assembled interface structure. Our structural analysis at an atomic level by using high-angle annular dark-field scanning transmission electron microscopy and energy dispersive X-ray spectrometry reveals that very thin layers of LuFe2O4 lacking Fe–O layers, corresponding to the hexagonal LuFeO3 and Lu2Fe3O7 compositions, are formed at the interface between the c-axis oriented LuFe2O4 thin film and YSZ substrate with a Lu-rich region just on the surface of the substrate. Such an interfacial structure leads to an exchange bias effect peculiarly observed for an interface formed by different types of magnetic materials. The LuFe2O4 thin film itself shows spin glass transition similar to bulk LuFe2O4 with an off-stoichiometric oxygen ratio. Also, a change in electronic transport behavior between Arrhenius-type and variable range hopping schemes has been observed in the temperature dependence of electrical resistivity around the three-dimensional charge ordering temperature.
Doping evolution of the unconventional superconducting properties in BaBiO3-based compounds has yet to be clarified in detail due to the significant change of the oxygen concentration accompanied by the chemical substitution. We suggest that the carrier concentration of an unconventional superconductor, BaPb0.7Bi0.3O3−δ, is controllable without inducing chemical or structural changes using an electric double-layer transistor structure. The critical temperature is found to decrease systematically with increasing carrier concentration.