Observation of a Novel Orbital Selective Mott Transition inCa1.8Sr0.2RuO4

We observed a novel orbital selective Mott transition in ${\mathrm{Ca}}_{1.8}{\mathrm{Sr}}_{0.2}{\mathrm{RuO}}_4$ by angle-resolved photoemission. While two sets of dispersing bands and the Fermi surface associated with the doubly degenerate $d_{yz}$ and $d_{zx}$ orbitals are identified, the Fermi surface associated with the wider $d_{xy}$ band is missing as a consequence of selective Mott localization. Our theoretical calculations demonstrate that this orbital selective Mott transition is mainly driven by the combined effects of interorbital carrier transfer, superlattice potential, and orbital degeneracy, whereas the bandwidth difference plays a less important role.