Seminarium Fizyki Materii Skondensowanej

The effect of electronic correlation is important to correctly describe the compounds with partially filled d-f shells; e.g. transition metal oxides, actinides, high Tc superconductors etc. Correlation effects give rise to a host of novel phenomena, e.g. Mott metal to insulator transition, excitonic phase transition, colossal magnetoresistance etc. The density functional theory (DFT) fails to properly account for the correlation effects and hence cannot explain these phenomena. Correlations can be modeled using the DFT+U, where U is the Coulomb interaction, or DFT+DMFT (Dynamical Mean Field Theory). It is shown for the 5f intermetallic compound UGa2, DFT+DMFT can reproduce the experimental X-ray absorption spectra, photo-emission spectra, and magnetic moments better than DFT+U for an optimized choice of spin polarized double counting.As a separate problem, it is discussed how DMFT in a real space (R- DMFT) within some additional approximation can describe Friedel oscillations (FO) in finite lattice systems in the presence of charged impurities for metallic, insulating and Mott insulating regime solving an inhomogeneous one band Hubbard model. Charged impurities are modeled using a single impurity potential, two, multiple discreet impurities, extended inhomogeneties, and a chain of impurities representing a domain wall. In each case, FO is damped with the interactions and disappears at the Mott transition. Interference patterns are seen on FO for two or more impurities and they are dependent on the lattice geometry. These model studies could be useful to understand the role of defects, dopants in transition metal oxides which are the target functional materials for the future Mott transistors. For seminar link contact Pawel Jakubczyk by email.