Angle-resolved photoemission spectroscopy of non-cuprate two-dimensional perovskite superconductor Sr₂RuO₄

We have performed high-resolution angle-resolved photoemission spectroscopy on single crystal Sr₂RuO₄. at low temperature. We observed that the dispersion of energy bands near the Fermi level (E_F) is about two times smaller than the band calculation. One band forms an extended van-Hove singularity (vHs) near E_F around the midpoint between F and Z point like in cuprate superconductors, regardless of the character of electronic states near E_F. The observed Fermi surface topology (one electron-like Fermi surface sheet centered at Γ point and two hole-like ones centered at X point) is qualitatively different from the calculated Fermi surface topology (two electron-like fermi sheets centered at Γ point and one hole-like one centered at X point), though the observed total electron count seems to be conserved. These results suggest that the extended vHs may be a general electronic structure of correlated two-dimensional metals and the correlation effect may change the Fermi surface topology as well as the band dispersion.