Fermi surface and extended van Hove singularity in the non-cuprate layered perovskite superconductor Sr₂RuO₄

Abstract

With high-resolution (≈22 meV) angle-resolved photoemission spectroscopy, the Fermi surface of the first copper free layered-perovskite superconductor, Sr₂RuO₄, was determined. We observed three bands to cross the Fermi energy in qualitative agreement with LDA band structure calculations; one electron-like surface encircling the$\overline \Gamma$ point in the projected Brillouin zone, and two hole-like surfaces around the$\overline X$ point. The most striking aspect of the measurements is the observation of an extended van Hove singularity. It is located 17 meV below the Fermi energy and extends around the$\overline M$ point for about 0.2 Å⁻¹ along both the$\overline \Gamma$ —$\overline M$ —$\overline \Gamma$ and the$\overline X$ —$\overline M$ —$\overline X$ directions.These observations demonstrate that van Hove singularities near the Fermi surface are a more generic feature of layered oxides, and call for a clarification of their exact role in oxide superconductivity.