Evidence for strong electronic correlations in the spectra of Sr${}_2$RuO${}_4$

The importance of electronic correlation effects in the layered perovskite Sr${}_2$RuO${}_4$ is evidenced. To this end we use state-of-the-art LDA+DMFT (Local Density Approximation + Dynamical Mean-Field Theory) in the basis of Wannier functions to compute spectral functions and the quasiparticle dispersion of Sr${}_2$RuO${}_4$. The spectra are found to be in good agreement with various spectroscopic experiments. We also calculate the $\mathbf{\text{k}}$-dependence of the quasiparticle bands and compare the results with new angle resolved photoemission (ARPES) data. Two typical manifestations of strong Coulomb correlations are revealed: (i) the calculated quasiparticle mass enhancement of $m^{\ast }\mathrm{/}m\approx 2.5$ agrees with various experimental results, and (ii) the satellite structure at about 3 eV binding energy observed in photoemission experiments is shown to be the lower Hubbard band. For these reasons Sr${}_2$RuO${}_4$ is identified as a strongly correlated 4$d$ electron material.