Electronic Structure of the BaFe$_2$As$_2$ Family of Iron Pnictides

Abstract

We use high resolution angle-resolved photoemission spectroscopy to study the band structure and Fermi surface topology of the BaFe2As2 iron pnictides. We observe two electron bands and two hole bands near the X-point, (π, π) of the Brillouin zone, in the paramagnetic state for different doping levels, including electron-doped Ba(Co0.06Fe0.94)2As2, undoped BaFe2As2, and hole-doped Ba0.6K0.4Fe2As2. Among these four bands, only the electron bands cross the Fermi level, forming two electron pockets around X, while the hole bands approach but never reach the Fermi level. We show that the band structure of the BaFe2As2 family matches reasonably well with the prediction of LDA calculations after a momentum-dependent shift and renormalization. Our finding resolves a number of inconsistencies regarding the electronic structure of pnictides.

Classification of the electronic correlation strength in the iron pnictides: The case of the parent compoundBaFe2As2

“…The other d-orbitals have a slightly larger value (m * /m = 2.05 -2.07). The overall effective mass enhancement m * /m ≈ 2 agrees well with the ARPES data for BaFe 2 As 2 [24,25]. It is also in good agreement with experimental results for the pnictide material LaFePO, where de Haas-van Alphen experiments [26] found a mass enhancement between 1.7 and 2.1, and ARPES [27] measured a band renormalization by a factor of 2.2 compared with the LDA.…”

Fermi-Surface Shrinking and Interband Coupling in Iron-Based Pnictides

“…Note that such self-energy corrections due to the particle-hole asymmetry survive until energies much larger than ω 0 , so that the energy shift is effective also at momenta far from the Fermi level. In particular this means that, when interband interactions are predominant, the top of the hole bands (at Γ) and the bottom of the electron bands (at M ) approach each other with respect to the prediction of LDA, in agreement with the ARPES observation in 122 compounds [10,11,12,13]. Note also in Fig.…”

“…Since determining the Fermi surface topology is the first step toward the understanding of these new materials, a lot of experimental work has been devoted to its investigation. A momentum-resolved mapping of the dispersion of the occupied quasi-particle states in the normal state and in the superconducting one has been provided by angle-resolved photoemission spectroscopy (ARPES), both in 1111 [8] and 122 systems [9,10,11,12,13]. An alternative technique probing the Fermi surface topology, which is not momentum resolved but has the advantage of being a bulk probe, is based on de Haas-van Alphen (dHvA) magnetization measurements, which allow one to estimate the size of the Fermi areas and the effective mass m * for each Fermi sheet [14,15,16,17,18].…”

“…Notably, such shifts have different signs in hole and electron bands, being downward for the hole-band and upward for the electron ones [14,15]. This effect seems to persist to higher energies, as one can infer from ARPES, which gives a systematical reduction of the energy difference between the bottom of the electron bands and the top of the hole bands with respect to the values predicted by LDA [10,11,12,13]. Even though a certain degree of inaccuracy could be present in density-functional theory calculations, the persistent observations of such shifts suggests a robust feature in these materials whose origin is at the moment unknown.…”

Angle-Resolved Photoemission Spectroscopy of the Iron-Chalcogenide SuperconductorFe1.03Te0.7Se0.3: Strong Coupling Behavior and the Universality of Interband Scattering

“…This opposite shift between the hole and the electron pockets cannot be simply explained in terms of electron doping by the presence of excess Fe atoms. Interestingly, a similar behavior has been reported for FeP (iron-phosphorous)- [36] and FeAs-based [35,37] superconductors, suggesting that it is a general trend of Fe-based superconductors.…”