Strontium ruthenate (Sr2RuO4) forms a layered perovskite structure. As shown in the upper panel, the crystal's RuO2 layers are separated by Sr layers, and each Ru ion is enclosed in an octahedral cage of oxygen ions.  The same structure is also found in La2CuO4, which is the parent compound of the high-Tc superconductor La2-xBaxCuO4.  Despite their structural similarity, the ruthenate and the cuprate have very different electronic properties: Sr2RuO4 is strongly metallic and a superconductor at low temperature, whereas La2CuO4 is an antiferromagnetic insulator.  The lower panel shows the configuration of the orbitals responsible for the superconductivity of Sr2RuO4, namely, the 4d t2g orbitals
Strontium ruthenate
The superconducting states