Fermi surface topology of Ca₁.₅Sr₀.₅RuO₄ determined by ARPES

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We report ARPES results of the Fermi surface of Ca₁.₅Sr₀.₅RuO₄, which is at the boundary of magnetic/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three t₂g energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free Sr₂RuO₄. We find that while the Fermi surface topology of the alpha, beta (dyz, zx) sheets remains almost the same in these two materials, the gamma (dxy) sheet exhibits a hole-like Fermi surface in Ca₁.₅Sr₀.₅RuO₄ in contrast to being electron-like in Sr₂RuO₄. Our observation of all three volume conserving Fermi surface sheets clearly demonstrates the absence of orbital-selective Mott transition, which was proposed theoretically to explain the unusual transport and magnetic properties in Ca₁.₅Sr₀.₅RuO₄.