Optical Response of Sr2RuO4 Reveals Universal Fermi-Liquid Scaling and Quasiparticles Beyond Landau Theory

We report optical measurements demonstrating that the low-energy relaxation rate (1/tau) of the conduction electrons in Sr2RuO4 obeys scaling relations for its frequency (omega) and temperature (T) dependence in accordance with Fermi-liquid theory. In the thermal relaxation regime, 1/tau proportional to ((h) over bar omega)(2) + (p pi k(B)T)(2) with p = 2, and omega/T scaling applies. Many-body electronic structure calculations using dynamical mean-field theory confirm the low-energy Fermi-liquid scaling and provide quantitative understanding of the deviations from Fermi-liquid behavior at higher energy and temperature. The excess optical spectral weight in this regime provides evidence for strongly dispersing resilient quasiparticle excitations above the Fermi energy.