Electronic band structure of the superconductor ${\mathrm{Sr}}_2$${\mathrm{RuO}}_4$

A local-density electronic-band-structure calculation was performed for a recently discovered non-copper-layered perovskite superconductor, ${\mathrm{Sr}}_2$${\mathrm{RuO}}_4$. It was found that the electronic structure near the Fermi energy is essentially described by antibonding bands of the Ru dɛ and O pπ states. Although two holes in the bands are predominantly situated in a dɛ(xy)-pπ state in the ab plane, the hole occupations in the other dɛ-pπ states vertical to the plane are not negligibly small, possibly in conjunction with the smallness of tetragonal distortion of the ${\mathrm{RuO}}_6$ octahedron. Associated with the antibonding dɛ-pπ bands, the density of states at the Fermi energy is relatively high (4.36 states/eVcell) but not enough to account for the observed specific-heat constant ${\gamma }_{\exp }$ and temperature-independent magnetic susceptibility ${\mathrm{\chi }}_{\exp }$. We found a large Stoner factor, which may explain most of the mass enhancement involved in ${\mathrm{\chi }}_{\exp }$. Certain similarities and dissimilarities in the electronic properties to the cuprate superconductors are discussed.