Executive Summary : | This study focuses on studying the properties of CaRuO₃ and SrRuO₃ ruthenate films by tuning the epitaxial strain. The epitaxial strain in 4d ferromagnet SrRuO₃ films is directly linked to the physical properties through the strong coupling between lattices, electrons, and spins, providing an excellent opportunity to tune the functionalities of these systems in electronic and spintronic devices. However, a thorough understanding of the epitaxial strain effect in these systems has remained elusive due to the lack of systematic studies. The strain can be developed by fabricating films on various lattice mismatch substrates. Ruthenates exhibit the metallic state due to large electronic bandwidth compared to electronic correlations and are the subject of contemporary interest in the context of observation of the breakdown of the Fermi liquid ground state. SrRuO₃ exhibits unusual itinerant ferromagnetism, while CaRuO₃ is close to ferromagnetic instability. Recent advancements have been made to explore the material's properties in the THz energy range, using emergent techniques of time-domain THz spectroscopy to probe electron-electron interactions at low energy and calculate the optical conductivity response function at temperatures as low as 1.5K. An extended Drude model analysis will be used to construct a picture of the turning-on of correlations as the temperature is lowered, and the frequency-dependent scattering rate and renormalized mass from T=1.5-300K will be calculated. Combining this analysis with power-law fits will investigate the extent to which these materials obey Fermi liquid theory and quantify any possible deviations. |