High Tc superconductivity at the interface between the CaCuO2 and SrTiO3 insulating oxides

摘要

At interfaces between complex oxides it is possible to generate electronicsystems with unusual electronic properties, which are not present in theisolated oxides. One important example is the appearance of superconductivityat the interface between insulating oxides, although, until now, with very lowTc. We report the occurrence of high Tc superconductivity in the bilayerCaCuO2/SrTiO3, where both the constituent oxides are insulating. In order toobtain a superconducting state, the CaCuO2/SrTiO3 interface must be realizedbetween the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this caseextra oxygen ions can be incorporated in the interface Ca plane, acting asapical oxygen for Cu and providing holes to the CuO2 planes. A detailed holedoping spatial profile has been obtained by STEM/EELS at the O K-edge, clearlyshowing that the (super)conductivity is confined to about 1-2 CaCuO2 unit cellsclose to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3interface can be extended to multilayered high Tc cuprates, contributing toexplain the dependence of Tc on the number of CuO2 planes in these systems.