Anisotropic properties of a single superconducting CaCuO2/SrTiO3 interface

The transport properties of CaCuO2/SrTiO3 single interfaces are studied by resistance versus temperature measurements in external magnetic fields. The superconducting anisotropy gamma=xi(a-b)/xi(c), where xi(a-b) and xi(c) are the superconducting coherence lengths parallel and perpendicular to the interface, respectively, shows values higher than that previously obtained for CaCuO2/SrTiO3 superlattices deposited in the same conditions. The larger anisotropy, observed for the single interfaces, indicates that the charge carriers are confined inside a thin superconducting layer next to the interface rather than spread throughout the whole CaCuO2 block. The activation energy and the irreversibility line confirm this hypothesis, suggesting that quasi two-dimensional transport is dominant in this system. The interpretation of the experimental data in the framework of the Berezinskii-Kosterlitz-Thouless theory confirms that the thickness of the superconducting sheet layer is about 1 nm, corresponding roughly to two CaCuO2 unit cells.