High-resolution, hard x-ray photoemission investigation ofBaFe2As2: Moderate influence of the surface and evidence for a low degree ofFe

Abstract

Photoemission data taken with hard x-ray radiation on cleaved single crystals of the barium parent compound of the MFe 2 As 2 pnictide high-temperature superconductor family are presented. Making use of the increased bulk sensitivity upon hard x-ray excitation, and comparing the results to data taken at conventional vacuum ultraviolet photoemission excitation energies, it is shown that the BaFe 2 As 2 cleavage surface provides an electrostatic environment that is slightly different to the bulk, most likely in the form of a modified Madelung potential. However, as the data argue against a different surface doping level, and the surface-related features in the spectra are by no means as dominating as seen in systems such as YBa 2 Cu 3 O x , we can conclude that the itinerant, near-E F electronic states are almost unaffected by the existence of the cleavage surface. Furthermore, exploiting the strong changes in photoionization cross section between the Fe and As states across the wide photon energy range employed, it is shown that the degree of energetic overlap between the iron 3d and arsenic 4p valence bands is particularly small at the Fermi level, which can only mean a very low degree of hybridization between the Fe 3d and As 4p states near and at E F . Consequently, this means that the itinerancy of the charge carriers in this group of materials involves mainly the Fe 3d-Fe 3d overlap integrals with at best a minor role for the Fe 3d-As 4p hopping parameters and that the states which support superconductivity upon doping are essentially of Fe 3d character.

Scanning tunneling microscopy and spectroscopy on iron-pnictides

“…The predominance of the latter scenario is substantiated by Fermi surface volume measurements from ARPES studies of BaFe 2 As 2 [43,44].…”

Dynamical screening in correlated electron systems—from lattice models to realistic materials

“…Indeed, as shown in the middle panel (inset), we can identify these peaks in the spectral function computed with the procedure described in Sec. V. It is interesting to note that a satellite at approximately −6.5 eV has been seen in photoemission experiments [139,140].…”

Dynamical Correlations and Screened Exchange on the Experimental Bench: Spectral Properties of the Cobalt PnictideBaCo2As2

“…The discovery of unconventional superconductivity in iron pnictides and chalcogenides in 2008 has aroused strong interest into the Fermi surfaces and low-energy excitations of transition metal pnictides and related compounds. Angle-resolved photoemission spectroscopy (ARPES) has been used to systematically map out quasiparticle dispersions, and to identify electron and hole pockets potentially relevant for low-energy instabilities [1][2][3][4][5][6][7]. Density functional theory (DFT) calculations have complemented the picture, yielding information about orbital characters [8], or the dependence of the topology of the Fermi surface on structural parameters or element substitution [9,10].…”