The fate of quasiparticles at high-temperature

Abstract

We study the temperature evolution of quasiparticles in the correlated metal Sr${}_2$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 Sr${}_2$RuO${}_4$ not by losing weight but via excessive broadening from super-Planckian scattering. We further show that the Fermi surface of Sr${}_2$RuO${}_4$ - defined as the loci where the spectral function peaks - deflates with increasing temperature. These findings are in semi-quantitative agreement with dynamical mean field theory calculations.

Supplemental Material available upon request