Using the generalized gradient approximation plus dynamical mean-field theory (GGA+DMFT) we confirm the importance of multi-orbital dynamical correlations in determining the paramagnetic insulating state of CrI3. While the ferromagnetic phase reveals weak electronic correlation effects due to strong spin-orbital polarization, the Mott insulating state of paramagnetic CrI3 crystal is shown to be driven by the interplay between orbital-dependent one-electron lineshape and multi-orbital electronic interactions. To probe the paramagnetic Mott insulating state we performed x-ray absorption spectroscopy (XAS) measurements for the two structural phases of CrI3. Our study is relevant to understanding the orbital-selective electronic structure reconstruction of Mott insulators and should be applicable to other van der Waals bonded materials from bulk to the ultrathin limit.

We perform a comprehensive analysis of both the chemical and correlated electronic structure reconstruction of rhombohedral CrX3 (X=Br, Cl, I) van der Waals bulk crystals. Using the generalized gradient approximation (GGA) plus dynamical mean-field theory we explicitly demonstrate the importance of local dynamical correlations for a consistent understanding of emergent Kondo quasiparticles and Mott localized electronic states, showing the interplay between material-dependent one-electron GGA line-shape and multiorbital electronic interactions. To probe the correlated paramagnetic electronic state we performed x-ray absorption spectroscopy measurements for CrCl3 and CrBr3 bulk crystals. Our correlated many-body study is relevant to understanding the electronic structure reconstruction of paramagnetic Cr-trihalide crystals and should be widely applicable to other van der Waals magnetic materials.

The van der Waals (vdW) chromium trihalides (CrX₃) exhibit field-tunable, two-dimensional magnetic orders that vary with the halogen species and the number of layers. Their magnetic ground states with proximity in energies are sensitive to the degree of ligand-metal (p-d) hybridization and relevant modulations in the Cr d-orbital interactions. We use soft X-ray absorption (XAS) and resonant inelastic X-ray scattering (RIXS) spectroscopy at Cr L-edge along with the atomic multiplet simulations to determine the key energy scales such as the crystal field 10 Dq and interorbital Coulomb interactions under different ligand metal charge transfer (LMCT) in CrX₃ (X= Cl, Br, and I). Through this systematic study, we show that our approach compared to the literature has yielded a set of more reliably determined parameters for establishing a base Hamiltonian for CrX₃.

We describe the local structural properties of the iron oxychalcogenides, La2O2Fe2OM2(M=S,Se), by using pair distribution function analysis applied to total scattering data. Our results from neutron powder diffraction show that M = S and Se possess similar nuclear structures at low and room temperatures. The local crystal structures were studied by investigating deviations in atomic positions and the extent of the formation of orthorhombicity. Analysis of the total scattering data suggests that buckling of the Fe2O plane occurs below 100 K. The buckling may occur concomitantly with a change in octahedral height. Furthermore, within a typical range of 1-2 nm, we observed a short-range orthorhombiclike structure suggestive of nematic fluctuations in both of these materials.

We present the results of structural and magnetic phase comparisons of the iron oxychalcogenides La2O2Fe2OM2(M=S,Se). Elastic neutron scattering reveals that M=S and Se have similar nuclear structures at room and low temperatures. Our neutron diffraction data reveals that both materials obtain antiferromagnetic ordering at a Néel temperature TN90.1±0.16 K and 107.2±0.06 K for M=Se and S, respectively. The magnetic arrangements for both M=S, Se compounds are obtained through Rietveld refinement. We find the order parameter exponent β to be 0.129±0.006 for M=Se and 0.133±0.007 for M=S. Each of these values is near the Ising symmetry value of 1/8. This suggests that although lattice and electronic structural modifications result from chalcogen replacement, the nature of the magnetic interactions is similar in these materials.