Fig. 5: Calculated imaginary part of the susceptibility χ₀(ω, q_∣∣, q_⊥ = 0) (second column), loss function \(\Im \left\{-\frac{1}{\epsilon (\omega,{q}_{| | },{q}_{\perp }=0)}\right\}\) (third column), and plasmon dispersion (fourth column) along the momentum (q_∣∣, q_⊥ = 0).

In the calculation various effective masses were used: first row m^*/m₀ = 1, second row m^*/m₀ = 3.5, and an energy dependent effective mass m^*(ω)/m₀ shown in the third row. The red labels in the susceptibility in the first row are related to the origin of the three electronic bands in Sr₂RuO₄. In column four we compare the experimental optical plasmon dispersion (shown in Fig. 4) with the calculated one for m^*/m₀ = 1 and 3.5, and a band structure which is renormalized only at low energies. The horizontal error bars originate from the finite momentum resolution while the vertical ones are related to the finite spectral resolution of the EEL spectrometer.