Effective masses, lifetimes, and optical conductivity in Sr2RuO4 and Sr3Ru2O7 : Interplay of spin-orbit, crystal-field, and Coulomb tetragonal tensor interactions

Abstract

By using the local-density approximation + dynamical mean-field theory approach, we study the low-energy electronic properties and the optical conductivity of the layered ruthenates ${\mathrm{Sr}}_{2}{\mathrm{RuO}}_{4}$ and ${\mathrm{Sr}}_{3}{\mathrm{Ru}}_{2}{\mathrm{O}}_{7}$. We study the interplay of spin-orbit, crystal-field, and Coulomb interactions, including the tetragonal terms of the Coulomb tensor. We show that the spin-orbit interaction is multifaced; depending on the parameter regime, filling, and temperature, it can either enhance or reduce the effective strength of correlations. We compare the results based on the two common approximations for the screened Coulomb parameters, the constrained random-phase approximation (cRPA) and the constrained local-density approximation. We show that the experimental Drude peak is better reproduced by the cRPA parameters, hinting to relatively small mass renormalizations. We find that including the spin-orbit interaction is, however, important, for a realistic description. We show that Coulomb terms with tetragonal ${D}_{4h}$ symmetry have a strong effect on the mass-enhancement anisotropy, but they do not affect sizably the total spectral function or the in-plane conductivity.