The effects of electron-electron correlations on the low-energy electronic structure and their relationship with unconventional superconductivity are central aspects in the research on the iron-based pnictide superconductors. Here we use soft X-ray a
ngle-resolved photoemission spectroscopy (SX-ARPES) to study how electronic correlations evolve in different chemically substituted iron pnictides. We find that correlations are intrinsically related to the effective filling of the correlated orbitals, rather than to the filling obtained by valence counting. Combined density functional theory (DFT) and dynamical mean-field theory (DMFT) calculations capture these effects, reproducing the experimentally observed trend in the correlation strength. The occupation-driven trend in the electronic correlation reported in our work supports the recently proposed connection between cuprate and pnictides phase diagrams.
Temperature dependence of the electronic structure of SmB6 is studied by high-resolution ARPES down to 1 K. We demonstrate that there is no essential difference for the dispersions of the surface states below and above the resistivity saturating anom
aly (~ 3.5 K). Quantitative analyses of the surface states indicate that the quasi-particle scattering rate increases linearly as a function of temperature and binding energy, which differs from Fermi-Liquid behavior. Most intriguingly, we observe that the hybridization between the d and f states builds gradually over a wide temperature region (30 K < T < 110 K). The surface states appear when the hybridization starts to develop. Our detailed temperature-dependence results give a complete interpretation of the exotic resistivity result of SmB6, as well as the discrepancies among experimental results concerning the temperature regions in which the topological surface states emerge and the Kondo gap opens, and give new insights into the exotic Kondo crossover and its relationship with the topological surface states in the topological Kondo insulator SmB6.
