thin film*

Understanding the metallic normal state of Sr₂RuO₄ could help solve puzzles about its unconventional superconducting state. The normal state of Sr₂RuO₄ is considered a clean Fermi liquid in the low temperature and low frequency limit. Herein we present time domain THz measurements of the optical conductivity of a highly clean, RRR (residual resistivity ratio) ≈ 53 epitaxial thin film, in which we find deviation from Fermi liquid scaling of a simple metal below 3 meV. The complex conductivity can be modeled with two Drude terms, the decay rate of both of which follows T^2 dependence. We discuss the physical implications of two conducting channels. We compare the results with our experiments on other metallic ruthenates including SrRuO₃ and CaRuO₃ with similar RRR.