Invited Talk: Jernej MravljeSpectroscopies of Hund's metals within (DFT+)DMFT: electronic Raman response in Sr₂RuO₄

Spectrocopically, Hund's metals (e.g. ruthenates, iron-based superconductors) are characterized by multiplet splittings of the Hubbard bands and a particular shape of the quasiparticle peak associated to a two-stage screening of the spin and orbital momentums. We recently found another feature, stemming from strong charge fluctuations in Hund's metals, which leads to a side-peak at energy given exclusively by the value of Hund's rule coupling, that I will discuss based on dynamical mean-field theory results for a three orbital model Hund's metal. I will discuss the appearance of those features in photoemission and optical spectroscopies.

Another characteristics of Hund's metals in general and of the normal state of the unconventional superconductor Sr₂RuO₄ in particular is the strong orbital differentiation. Raman scattering allows in principle to access the response associated to different orbitals by coupling to light in different polarization channels. We calculate electronic Raman response of Sr₂RuO₄ using a combination of density-functional theory and dynamical mean-field theory methods. We calculated the Raman vertex tensors within the effective mass approximation. We found considerably different response in the B_1g and B_2g channels, with less coherent response found in the B_2g channel that is nominally sensitive to the more correlated xy orbital (and associated γ Fermi surface sheet), consistent with measurements of Philippe et al., Phys. Rev. B 103, 235147 (2021). However, precise investigation of different contributions to the response points to important interband couplings enhanced by the finite-frequency nesting between γ and β Fermi surface sheets, which strongly influence the response in the B2g channel. Our results indicate the importance of realistic first-principle based approaches in the interpretation of electronic Raman spectroscopies.