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Hyowon Park: Understanding strong correlations of quantum materials from first-principles

Assistant Professor, Department of Physics, University of Illinois at Chicago

Materials Science Division, Argonne National Lab

Strongly correlated materials are promising candidates for future applications since their emergent electronic properties such as the Mott transition, spin-state transition, charge ordering, and superconductivity are strongly coupled to each other. One of the grand challenges in modern material science is the theoretical understanding of strong correlations occurring in quantum materials using first-principles. Dynamical mean field theory (DMFT) has been a successful first-principles method for the study of the electronic structure in strongly correlated materials, especially when it is combined with density functional theory (DFT). In this talk, I will present the DFT+DMFT study of various strongly correlated materials obtained from first-principles. First, I will introduce our free-licensed DFT+DMFT code implemented using the maximally localized Wannier orbital, also effectively interfaced to various DFT codes. Then, I will show DFT+DMFT results of different transition-metal oxide materials including LaCoO3 exhibiting the spin-state transition, LaNiO3 with oxygen vacancies, and electron- or hole-doped NiO. We found that the homogeneous spin-state excitation in bulk LaCoO3 at elevated temperature shows the dynamically fluctuating nature of high-spin and low-spin configurations accompanied by the volume expansion. We also stabilized the mixed spin-state phase with alternating high-spin and low-spin phases accompanied by the charge ordering as shown in the resonant X-ray scattering experiment of tensile strained film. Oxygen vacancy plays an important role in LaNiO3 as the metal-to-insulator transition occurs accompanied by magnetism as the oxygen vacancy level gets increased. Using DFT+DMFT, we studied the change of electronic structure in LaNiO3 with oxygen vacancy and successfully compared to data measured in photo-emission spectroscopy and X-ray absorption spectroscopy experiments. We clarified the nature of the insulating state in vacancy-ordered LaNiO2.5 as the site-selective Mott phase occurs from both structural and charge-transfer effects of oxygen vacancies, which cannot be explained from the result of the rigid band shift based on the homogeneous vacancy scenario. We also compared electronic structure of doped NiO to the optical spectra measurement and found a good agreement with experiment.