Electronic correlations and transport in multi-orbital systemsHorvat, Alen (Avtor) Mravlje, Jernej (Mentor) multi-orbital impurity modelsKondo effectHund’s metalsspin-orbit couplingtransport propertiesnumerical renormalization groupWe investigate electronic correlations and transport in multi-orbital models with Hund’s rule coupling. Recent theoretical investigations of multi-orbital models pointed out the vital role of the Hund’s rule coupling, which induces strong correlations away from the Mott transition, suppresses the coherence scale and causes a two-stage Kondo screening. These properties were also observed experimentally in ruthenates and pnictides, which are hence called Hund’s metals. Impurity models play a central role in the dynamical mean-field theory, where we map the problem of the bulk to an impurity problem coupled to a self-determined bath. However, the multi-orbital impurity models are, in contrast to single-orbital impurity models, poorly understood. We investigate in detail the multi-orbital Anderson impurity model with Kanamori and Dworin-Narath interactions. First, we derive the corresponding Kondo models using the Schrieffer-Wolff transformation and apply the perturbative renormalization group theory to investigate their low-temperature properties. The Hund’s impurity undergoes a two-stage Kondo screening process, where the orbital degrees of freedom are screened at higher temperatures than the spin. Next, we solve the impurity problem with the numerical renormalization group impurity solver. We extend the solver to take advantage of the symmetry of the problem. We address the Kondo model and investigate the fixed points and their effects on impurity spectral functions. Last, we consider the spin-orbit coupling and show that the spin-orbit coupling affects the physics of the model only at temperatures above the orbital Kondo temperature. In the second part, we investigate the multi-orbital model on Bethe lattice within DMFT. We use the NRG impurity solver to calculate the spectral functions and transport properties, i.e., the temperature dependence of the Seebeck coefficient and resistivity. In the last part, we investigate the transport properties of the single-orbital Kondo-Hubbard model.20192019-09-05 07:15:03Doktorsko delo/naloga109521VisID: 98044COBISS_ID: 3336548sl