Three-Dimensional Electronic Structure of Superconducting Iron Pnictides Observed by Angle-Resolved Photoemission Spectroscopy

Abstract

We have performed an angle-resolved photoemission spectroscopy (ARPES) study of the undoped and electron-doped iron pnictides BaFe 2−x Co x As 2 (Ba122) (x=0, 0.14) and studied the Fermi surfaces (FSs) and band dispersions near the Fermi level. The FS sheets we observed are consistent with the shrinkage of the hole-like pockets around the Brillouin Zone (BZ) center and the expansion of the electron pockets around the BZ corner in the electrondoped compound as compared to the undoped parent compound. Band dispersions and FSs around the BZ center strongly depend on the photon energy, indicating the three-dimensional (3D) electronic structure. This observation suggests that the antiferromagnetism and superconductivity in the pnictides may have to be considered including the orbital-dependent 3D electronic structure, where FS nesting is not necessarily strong.The discovery of superconductivity (SC) in layered iron pnictides 1 with the critical temperature T c reaching ∼56 K 2 has opened a new route for the high-T c research in addition to that of the cuprates, bringing new challenges to the materials science community on both experimental and theoretical sides.This new class of iron-based systems share some common properties with the cuprates such as the layered crystal structures 1 and antiferromagnetic (AFM) ordering in the parent compounds. 3, 4 However, many differences exist between the two families especially in their electronic structures. These differences started to appear from the early stage when local-density-approximation (LDA) band-structure calculations predicted that all the Fe 3d-derived bands exist near the Fermi level (E F ), resulting in complicated hole-and electron-like Fermi surface (FS) sheets, 5-7 whereas only a single band with one FS

Potential Antiferromagnetic Fluctuations in Hole-Doped Iron-Pnictide Superconductor Ba1-xKxFe2As2 Studied by 75As Nuclear Magnetic Resonance Measurement

“…In contrast, in BKFA electron Fermi surfaces do not completely disappear with hole doping, but their density of states near Fermi level still exist with further doping until x =1. This is confirmed by ARPES measurements 36,38,[53][54][55][56] and also by band structure calculation. 17,35) The recovery of increase of the 1/T 1 T at low temperatures in x = 1 is also indirect evidence for the specific band structure of hole-doped system.…”

The puzzle of high temperature superconductivity in layered iron pnictides and chalcogenides

“…This dispersion was confirmed from ARPES measurements by other groups on crystals of the same system. 154,155 Another important point regarding these measurements is that the observation of k z -axis hole band dispersion proves that the ARPES measurements on the 122-type FeAs-based compounds, which probe only ∼ 3-5Å into a material, are reflecting bulk properties of the material.…”

ARPES view of orbitally resolved quasiparticle lifetimes in iron pnictides

“…[12,13]. The general electronic structure has already been studied in some details by ARPES, both for Co8 [5,[22][23][24] and LiFeAs [10,25,26]. We add here more focused information on the separation of hole and electron bands of different orbital character and their linewidths.…”