Regensburg 2022 – wissenschaftliches Programm
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MA: Fachverband Magnetismus
MA 38: Electron Theory of Magnetism and Correlations
MA 38.4: Vortrag
Freitag, 9. September 2022, 10:15–10:30, H43
A Theory for Colors of Strongly Correlated Electronic Systems — •Swagata Acharya1, Cedric Weber2, Dimitar Pashov2, Mark van Schilfgaarde3, Alexander I Lichtenstein4, and Mikhail I Katsnelson1 — 1Radboud University, Nijmegen, The Netherlands — 2King's College London, London, UK — 3National Renewable Energy Laboratory, Colorado, US — 4Institute of Theoretical Physics, University of Hamburg, Germany
Many strongly correlated transition metal insulators are colored, even though they have large fundamental band gaps and no quasi-particle excitations in the visible range. We pick two archetypal cases as examples: NiO with green color and MnF2 with pink color. We show that a perturbative theory based on low-order extensions of the GW approximation is able to explain the color in NiO, and indeed well describe the dielectric response over the entire frequency spectrum, while the same theory is unable to explain why MnF2 is pink. We show its color originates from higher order spin-flip transitions that modify the optical response. This phenomenon is not captured by low-order perturbation theory, but is contained in dynamical mean-field theory (DMFT), which has a dynamical spin-flip vertex that contributes to the charge susceptibility. Within our combined self-consistent GW-BSE approximation and DMFT approach we can describe the peaks in subgap charge susceptibilities in both NiO and MnF2 . As a secondary outcome of this work, we establish that the one-particle properties of paramagnetic NiO and MnF2 are both well described by an adequate single Slater-determinant theory and do not require a dynamical vertex.