Fate of Quasiparticles at High Temperature in the Correlated Metal Sr2RuO4

We study the temperature evolution of quasiparticles in the correlated metal ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$. Our angle resolved photoemission data show that quasiparticles persist up to temperatures above 200 K, far beyond the Fermi liquid regime. Extracting the quasiparticle self-energy, we demonstrate that the quasiparticle residue $Z$ increases with increasing temperature. Quasiparticles eventually disappear on approaching the bad metal state of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ not by losing weight but via excessive broadening from super-Planckian scattering. We further show that the Fermi surface of ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$—defined as the loci where the spectral function peaks—deflates with increasing temperature. These findings are in semiquantitative agreement with dynamical mean field theory calculations.