We report on studies of charge carrier plasmon excitations in ${\mathrm{Sr}}_2{\mathrm{RuO}}_4$ by transmission electron energy-loss spectroscopy. In particular, we present results on the plasmon dispersion and its width as a function of momentum transfer. The dispersion can be qualitatively explained in the framework of random phase approximation calculations, using an unrenormalized tight-binding band structure. The constant long-wavelength width of the plasmon indicates that it is caused by a decay into interband transitions and not by quantum critical fluctuations. The results from these studies on a prototypical correlated metal system show that the long-wavelength plasmon excitations near 1 eV are caused by resilient quasiparticles and are not influenced by correlation effects.

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• Electronic structure
• Plasmons
• Strongly correlated systems
• Density functional calculations
• Electron energy loss spectroscopy
• Random phase approximation
• Tight-binding model