Fermi Surface, Surface States, and Surface Reconstruction inSr2RuO4
The electronic structure of ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ is investigated by high angular resolution ARPES at several incident photon energies. We address the controversial issues of the Fermi surface (FS) topology and the van Hove singularity at the $M$ point, showing that a surface state and the replica of the primary FS due to $\sqrt{2}\ifmmode\times\else\texttimes\fi{}\sqrt{2}$ surface reconstruction are responsible for previous conflicting interpretations. The FS thus determined by ARPES is consistent with the de Haas--van Alphen results, and it provides additional information on the detailed shape of the $\ensuremath{\alpha}$, $\ensuremath{\beta}$, and $\ensuremath{\gamma}$ sheets.