Fate of quasiparticles at high temperature in the correlated metal Sr₂RuO₄

We study the temperature evolution of quasiparticles in the correlated metal Sr2RuO4. 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 Sr2RuO4 not by losing weight but via excessive broadening from super-Planckian scattering. We further show that the Fermi surface of Sr2RuO4-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