The electronic structure of CeCoIn5 from angle-resolved photoemission spectroscopy II: Hybridization effects

We have investigated the low-energy electronic structure of the heavy fermion superconductor CeCoIn5 by angle-resolved photoemission. We focus on the dispersion and the peak width of the prominent quasi-two-dimensional Fermi surface sheet at the corner of the Brillouin zone as a function of temperature along certain k-directions with a photon energy of hn = 100 eV. We find slight changes of the Fermi vector and an anomalous broadening of the peak width when the Fermi energy is approached. Additionally we performed resonant ARPES experiments with hn = 121 eV. A flat f-derived band is observed with a distinct temperature dependence and a k-dependent spectral weight. These results, including both off- and on-resonant measurements, fit qualitatively to a two level mixing model derived from the Periodic Anderson Model.

Valence band and core level photoemission spectros-copy of LaFeAsO$_{1-x}$F$_{x}$

We have investigated the electronic structure of LaFeAsO$_{1-x}$F$_{x}$ (x = 0; 0.1; 0.2) by angle-integrated photoemission spectroscopy and local density approximation (LDA) based band structure calculations. The valence band consists of a low energy peak at E = -0.25 eV and a broad structure around E = -5 eV in qualitative agreement with LDA. From the photon energy dependence of these peaks we conclude that the former derives almost exclusively from Fe 3d states. This constitutes experimental evidence for the strong iron character of the relevant states in a broad window around EF and confirms theoretical predictions.