Electron correlation in the FeSe superconductor studied by bulk-sensitive photoemission spectroscopy

Abstract

We have investigated the electronic structures of recently discovered superconductor FeSe by soft-x-ray and hard-x-ray photoemission spectroscopy with high bulk sensitivity. The large Fe 3d spectral weight is located in the vicinity of the Fermi level (EF ), which is demonstrated to be a coherent quasi-particle peak. Compared with the results of the band structure calculation with local-density approximation, Fe 3d band narrowing and the energy shift of the band toward EF are found, suggesting an importance of the electron correlation effect in FeSe. The self energy correction provides the larger mass enhancement value (Z −1 ≃3.6) than in Fe-As superconductors and enables us to separate a incoherent part from the spectrum. These features are quite consistent with the results of recent dynamical mean-field calculations, in which the incoherent part is attributed to the lower Hubbard band.

Photoemission studies of the near EFspectral weight shifts in FeSe1−xTexsuperconductor

“…Fig 2) corresponds to the experimentally obtained features at 0.1 eV and 0.5 eV, respectively. The discrepancy in the energy positions could be due to the self-energy correction which is neglected in the calculations [24]. The partial density of states (PDOS) for Fe 3d orbitals for an energy range 0 -2.5 eV is represented in Fig.…”

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

“…This orbital differentiation signals that the material is in the vicinity of an orbital selective Mott transition, as proposed previously for other iron pnictides [14], where xy orbital is effectively insulating while other orbitals remain metallic. In Fig.1(b) we also display mass enhancement extracted from optics [15][16][17][18] and ARPES [19][20][21][22][23][24] measurements, and notice a good agreement between our theory and experiment when available. The effective mass extracted from ARPES and optics should be compared with that of the t2g orbitals which contribute most of the spectral weight at low energy.…”

X-Ray Spectroscopy Studies of Iron Chalcogenides

“…The Fe spectrum has a single line, which is narrower than the corresponding line of FeSe1-yTey. This dominant line in the spectrum of FeSe1-yTey is slightly broader than that of Fe, perhaps owing to Se hybridization state in the lower-energy region (Yamasaki et al, 2010;Subede et al, 2008). Iron pnictides are weakly correlated systems, unlike high-Tc cuprates.…”

“…Photoemission spectroscopy (PES) measurements (A. Yamasaki et al, 2010) support the density of state (DOS) calculations on the FeSex system. These results indicate the Fe-Se hybridization and itinerancy with weak to moderate electronic correlations (Yoshida et al, 2009), while recent theoretical calculations have suggested strong correlations (Aichhorn et al, 2010;Pourret et al, 2011).…”

“…The Se K-edge spectra reveal a hole increase with a decreasing x; however, no change in the Fe K-edge suggests a change in valence. According to the soft x-ray photoemission spectroscopy (XPS) measurements of Yamasaki et al (2010), the close distance between Se and Fe may increase the covalence of the Fe-Se bond due to the hybridization of Se 4p and Fe 3d states. Yoshida et al (2009) also observed an adequate correlation between their DOS calculations and the XPS spectra, which show a feature corresponding to the Fe 3d-Se 4p hybridization.…”