Alkaline-earth layer high-temperature superconductivity

Many experiments show that cuprate-planes are not needed for high-T-c superconductivity. For example, doped Ba2YRuO6 and Sr2YRuO6 superconduct at T-c similar to 93 K and similar to 49 K, have no cuprate-planes, and superconduct in their BaO and SrO planes. GdSr2-Cu2RuO8 and Gd2-zCezSr2Cu2RuO10 superconduct in their SrO layers, despite having non-superconducting cuprate-planes. Muon spectroscopy of YBa2Cu3O7 shows that its BaO layers superconduct, and its cuprate-planes do not. The superconductivity of YBa2Cu3O7 is s-wave, not d-wave, once flux-pinning is corrected for. Photoemission and scanning tunneling microscopy measurements correctly show the importance of the cuprate-planes, but do not show their superconductivity. Superconductivity is detected by muon spectroscopy of YBa2Cu3O7 and occupies the BaO layers, and not the cuprate-planes. Our work contradicts the cuprate-plane models of high-temperature superconductivity, and is fully consistent with specific heat and thermal conductivity measurements, which cuprate-plane models are not. (C) 2007 Elsevier B.V. All rights reserved.