Orbitally selective breakdown of Fermi liquid quasiparticles in Ca_1.8Sr_0.2RuO₄

We present a comprehensive angle-resolved photoemission spectroscopy study of Ca_1.8Sr_0.2RuO₄. Four distinct bands are revealed and along the Ru-O bond direction their orbital characters are identified through a light polarization analysis and comparison to dynamical mean-field theory calculations. Bands assigned to dxz,dyz orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions - associated with a predominantly dxy band character - are shown to display non-Fermi-liquid behavior. We thus demonstrate that Ca_1.8Sr_0.2RuO₄ is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.