EXTENDED VANHOVE SINGULARITY IN A NONCUPRATE LAYERED SUPERCONDUCTOR SR2RUO4

Angle-resolved photoemission spectroscopy was performed on a ruthenate superconductor Sr2RuO4 (T-c similar to 1 K) which has the same crysta l structure as La2CuO4, but with RuO2 layers replacing CuO2 layers. Sr 2RuO4 shows an extended Van Hove singularity (VHS) at 20 +/- 2 meV bel ow E(F) just like the cuprates, regardless of the character of the ele ctronic states at E(F). This suggests that the extended VHS is a gener al feature of a two-dimensional correlated d-electron metal. The obser ved Fermi surface is in contrast to local-density-approximation calcul ations.