Superconducting phase diagram in Ca2−xNaxCuO2Cl2−yBry

Ca2CuO2Cl2−yBry (0 ⩽ y ⩽ 2) has the K2NiF4-type structure with halogens (Cl and Br) at their apical sites and superconductivity can be achieved by substituting Ca2+ sites with Na+. We have succeeded in making a comprehensive superconducting phase diagram of Ca2−xNaxCuO2Cl2−yBry by focusing on special attention to the relationship between the superconductivity and the Cu and Cl/Br distance in Ca2−xNaxCuO2Cl2−yBry. We were successful in continuously changing the length of c-axis, which is closely related to the distance between the apical site and the CuO2 plane, or the distance between Cu and Cl/Br. Without changing the bonding distance between Cu and O in the CuO2 plane. This is the first example of this kind of control in cuprate superconductors.