Extended Van Hove Singularity in a Noncuprate Layered Superconductor Sr2RuO4

Abstract

Angle-resolved photoemission spectroscopy was performed on a ruthenate superconductor S${\mathrm{r}}_2$Ru${\mathrm{O}}_4$ ( $T_c\sim 1$ K) which has the same crystal structure as L${\mathrm{a}}_2$Cu${\mathrm{O}}_4$, but with Ru${\mathrm{O}}_2$ layers replacing Cu${\mathrm{O}}_2$ layers. S${\mathrm{r}}_2$Ru${\mathrm{O}}_4$ shows an extended Van Hove singularity (VHS) at $20\pm 2$ meV below $E_F$ just like the cuprates, regardless of the character of the electronic states at $E_F$. This suggests that the extended VHS is a general feature of a two-dimensional correlated d-electron metal. The observed Fermi surface is in contrast to local-density-approximation calculations.