My research focuses on how electrons organize according to their charge, spin, orbital and lattice degrees of freedom in order to exhibit novel phases of matter. A particular area of interest is iron-based superconducting materials and low-dimensional systems that exhibit emergent, quantum phenomena. This talk will discuss a combined experimental-theoretical study of quantum materials known as iron oxychalcogenides La2O2Fe2O(S,Se) 2, close cousins to the structurally similar to the iron pnictides but with a slightly increased iron unit cell. These materials are Mott insulators and their reduced kinetic energies, owing to narrowed Fe bands, are thought to lead to increased electron correlation. A combination of incoherent Hubbard features in x-ray absorption and resonant inelastic x-ray scattering spectra, as well as resistivity data, reveal that the parent oxychalcogenides are correlation-driven insulators. To uncover the microscopics underlying these findings, we performed local density approximation-plus-dynamical mean field theory (LDA+DMFT) calculations that reveaedl a novel Mott-Kondo insulating state. We also applied neutron diffraction in order to probe the establishment of long-range antiferromagenetic order. Neutron diffraction also indicates that global, structural C4 symmetry is preserved above and below Neel temperatures. However, local structure probes reveal C2 nematic fluctuations. Ideas will be presented on how the observed structural nematicity fits into the overall context of iron-based superconductivity. While, spin nematicity might manifest through geometrically frustrated magnetism and orbital selectivity, our findings highlight the interplay between orbital order and structural nematicity and the ubiquity of nematicity in strongly correlated Fe-based materials.
Speaker: Byron Freelon, University of Houston
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