Fermi Surface Topology of $Ca_{2-x}Sr_{x}RuO_4$ Determined by Angle-Resolved Photonelectron Spectroscopy

We report angle-resolved photoelectron spectroscopy results of the Fermi surface of $Ca_{1.5}Sr_{0.5}RuO_{4}$, which is at the boundary of magnetic/orbital instability in the phase diagram of the Ca-substituted Sr ruthenates. Three $t_{2g}$ energy bands and the corresponding Fermi surface sheets are observed, which are also present in the Ca-free $Sr_2RuO_4$.We find that while the Fermi surface topology of the $\alpha, \beta (d_{yz,zx})$ sheets remains almost the same in these two materials, the $gamma (d_{xy})$ sheet exhibits a holelike Fermi surface in $Ca_{1.5}Sr_{0.5}RuO_4$ in contrast to being electronlike in $Sr_2RuO_4$. 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 $Ca_{1.5}Sr_{0.5}RuO_{4}$. We will also report resent ARPES results on the samples with different Ca concentration.