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. (paper)