Relationship of ${\mathrm{Sr}}_2$${\mathrm{RuO}}_4$ to the superconducting layered cuprates

The properties of ${\mathrm{Sr}}_2$${\mathrm{RuO}}_4$ are discussed in relation to the high-critical-temperature cuprate superconductors. The discussion is based on local-density-approximation band structure and phonon calculations. The electronic structure is highly anisotropic. Three hybridized Ru 4d–plane O p bands cross the Fermi energy, yielding cylindrical sheets of Fermi surface. Two of these are electronlike sheets around Γ, while the third is an X-centered hole surface. The electronlike sheets change topology as the energy is raised leading to Van Hove singularities in close proximity to the Fermi energy. In general, the electronic properties are related to those of the cuprates, with the exception that Coulomb correlations are expected to be much less significant due to the larger bandwidth and smaller on-site energy. ${\mathrm{Sr}}_2$${\mathrm{RuO}}_4$ is expected to be a very useful reference material for interpreting experiments on the cuprate superconductors.