Orbitally selective breakdown of Fermi liquid quasiparticles in Ca${}_{1.8}$Sr${}_{0.2}$RuO${}_4$

Abstract

We present a comprehensive angle-resolved photoemission spectroscopy study of Ca${}_{1.8}$Sr${}_{0.2}$RuO${}_4$. 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 $d_{xz},d_{yz}$ orbitals display Fermi liquid behavior with fourfold quasiparticle mass renormalization. Extremely heavy fermions - associated with a predominantly $d_{xy}$ band character - are shown to display non-Fermi-liquid behavior. We thus demonstrate that Ca${}_{1.8}$Sr${}_{0.2}$RuO${}_4$ is a hybrid metal with an orbitally selective Fermi liquid quasiparticle breakdown.