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

TL;DR

This study demonstrates high-temperature superconductivity at the interface of two insulating oxides, CaCuO2 and SrTiO3, revealing the importance of interface chemistry and doping in inducing superconductivity.

Contribution

It reports the first observation of high Tc superconductivity at the interface between CaCuO2 and SrTiO3, highlighting the role of interface oxygen incorporation and hole doping.

Findings

Superconductivity is confined to 1-2 CaCuO2 unit cells near the interface.

Superconductivity occurs only when the interface is between Ca plane of CaCuO2 and TiO2 plane of SrTiO3.

The interface doping profile was mapped using STEM/EELS, confirming hole localization.

Abstract

At interfaces between complex oxides it is possible to generate electronic systems with unusual electronic properties, which are not present in the isolated oxides. One important example is the appearance of superconductivity at the interface between insulating oxides, although, until now, with very low Tc. We report the occurrence of high Tc superconductivity in the bilayer CaCuO2/SrTiO3, where both the constituent oxides are insulating. In order to obtain a superconducting state, the CaCuO2/SrTiO3 interface must be realized between the Ca plane of CaCuO2 and the TiO2 plane of SrTiO3. Only in this case extra oxygen ions can be incorporated in the interface Ca plane, acting as apical oxygen for Cu and providing holes to the CuO2 planes. A detailed hole doping spatial profile has been obtained by STEM/EELS at the O K-edge, clearly showing that the (super)conductivity is confined to about 1-2 CaCuO2 unit cells close to the interface with SrTiO3. The results obtained for the CaCuO2/SrTiO3 interface can be extended to multilayered high Tc cuprates, contributing to explain the dependence of Tc on the number of CuO2 planes in these systems.