Electronic Band Structure of Ferro-Pnictide Superconductors from ARPES Experiment (original) (raw)
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High-energy electronic interaction in the 3d band of high-temperature iron-based superconductors
Physical Review B, 2017
One of the most unique and robust experimental facts about iron-based superconductors is the renormalization of the electronic band dispersion by factor of 3 and more near the Fermi level. Obviously related to the electron pairing, this prominent deviation from the band theory lacks understanding. Experimentally studying the entire spectrum of the valence electrons in iron arsenides, we have found an unexpected depletion of the spectral weight in the middle of the iron-derived band, which is accompanied by a drastic increase of the scattering rate. At the same time, the measured arsenic-derived band exhibits very good agreement with theoretical calculations. We show that the low-energy Fermi velocity renormalization should be viewed as a part of the modification of the spectral function by a strong electronic interaction. Such an interaction with an energy scale of the whole d band appears to be a hallmark of many families of unconventional superconductors.
Electronic structure of Fe-based superconductors
Pramana, 2015
Fe-based superconductors have drawn much attention during the last decade due to the presence of superconductivity in materials containing the magnetic element, Fe, and the coexistence of superconductivity and magnetism. Extensive study of the electronic structure of these systems suggested the dominant role of d states in their electronic properties, which is significantly different from the cuprate superconductors. In this article, some of our studies of the electronic structure of these fascinating systems employing high-resolution photoemission spectroscopy is reviewed. The combined effect of electron correlation and covalency reveals an interesting scenario in their electronic structure. The contribution of ligand p states at the Fermi level is found to be much more significant than indicated in earlier studies. Temperature evolution of the energy bands reveals the signature of transition akin to Lifshitz transition in these systems.
Iron-based superconductors: Magnetism, superconductivity, and electronic structure (Review Article
Angle resolved photoemission spectroscopy (ARPES) reveals the features of the electronic structure of quasi-two-dimensional crystals which are crucial for spin and charge ordering and determine the mechanisms of electron-electron interactions, including superconducting pairing. The newly discovered iron-based superconductors (FeSC) promise interesting physics stemming, on one hand, from a coexistence of superconductivity and magnetism and, on the other, from a complex multi-band electronic structure.
Fermiology of 122 family of Fe-based superconductors: An ab initio study
Physics Letters A, 2014
Fermiology of various 122 systems are studied through first principles simulation. Electron doping causes expansion of electron and shrinkage of hole Fermi pockets. Isovalent Ru substitution (upto 35%) makes no visible modification in the electron and hole like FSs providing no clue regarding the nature of charge carrier doping. However, in case of 32% P doping there are considerable changes in the hole Fermi surfaces (FSs). From our calculations, it is very clear that two dimensionality of FSs may favour electron pair scattering between quasi-nested FSs which has important bearings in various orders (magnetic, orbital, superconducting) present in Fe-based superconductors.
2011
The discovery of high temperature superconductivity in the iron pnictide compound LaO1−xFxFeAs with Tc = 26K has created enormous interest in the high-Tc superconductor community. So far, four prototypes of crystal structures have been found in the Fe-pnictide family. All four show a structural deformation followed or accompanied by a magnetic transition from a high temperature paramagnetic conductor to a low temperature antiferromagnetic metal whose transition temperature TN varies between the compounds. Charge carrier doping, isovalent substitution of the As atoms or the application of pressure suppresses the antiferromagnetic spin density wave (SDW) order and leads to a superconducting phase. More recently high Tc superconductivity has been also detected in iron chalchogenides with similar normal state properties. Since superconductivity is an instability of the normal state, the study of normal state electronic structure in comparison with superconducting state could reveal impo...
Electronic origin of structural transition in 122 Fe based superconductors
Journal of Physics and Chemistry of Solids, 2017
Direct quantitative correlations between the orbital order and orthorhombicity is achieved in a number of Fe-based superconductors of 122 family. The former (orbital order) is calculated from first principles simulations using experimentally determined doping and temperature dependent structural parameters while the latter (the orthorhombicity) is taken from already established experimental studies; when normalized, both the above quantities quantitatively corresponds to each other in terms of their doping as well as temperature variations. This proves that the structural transition in Fe-based materials is electronic in nature due to orbital ordering. An universal correlations among various structural parameters and electronic structure are also obtained. Most remarkable among them is the mapping of two Fe-Fe distances in the low temperature orthorhombic phase, with the band energies E dxz , E dyz of Fe at the high symmetry points of the Brillouin zone. The fractional coordinate zAs of As which essentially determines anion height is inversely (directly) proportional to Fe-As bond distances (with exceptions of K doped BaFe2As2) for hole (electron) doped materials as a function of doping. On the other hand, Fe-As bond-distance is found to be inversely (directly) proportional to the density of states at the Fermi level for hole (electron) doped systems. Implications of these results to current issues of Fe based superconductivity are discussed.
A perspective on the Fe-based superconductors
Journal of Physics: Condensed Matter, 2010
FeSe is employed as reference material to elucidate the observed high T c superconducting behaviour of the related layered iron pnictides. The structural and ensuing semimetallic band structural forms are here rather unusual, with the resulting ground state details extremely sensitive to the precise shape of the Fe-X coordination unit. The superconductivity is presented as coming from a combination of Resonant Valence Bond (RVB) and Excitonic Insulator physics, and incorporating Boson-Fermion degeneracy. Although sourced in a very different fashion the latter leads to some similarites with the high temperature superconducting (HTSC) cuprates. The Excitonic Insulator behaviour sees spin density wave, charge density wave/periodic structural distortion (SDW, CDW/PLD), and superconductive instabilities all vie for ground state status. The conflict leads to a very sensitive and complex set of properties, frequently mirroring HTSC cuprate behaviour. The delicate balance between ground states is made particularly difficult to unravel by the microinhomogeneity of structural form which it can engender. It is pointed out that several other notable superconductors, layered in form, semimetallic with indirect overlap and possessing homopolar bonding, would look to fall into the same general category, β-ZrNCl and MgB 2 and the high-pressure forms of several elements, like sulphur, phosphorus, lithium and calcium, being cases in point.
In the family of the iron-based superconductors, the REFeAsO-type compounds (with RE being a rare-earth metal) exhibit the highest bulk superconducting transition temperatures (T c) up to 55 K and thus hold the key to the elusive pairing mechanism. Recently, it has been demonstrated that the intrinsic electronic structure of SmFe 0.92 Co 0.08 AsO (T c = 18 K) is highly nontrivial and consists of multiple band-edge singularities in close proximity to the Fermi level. However, it remains unclear whether these singularities are generic to the REFeAsO-type materials and if so, whether their exact topology is responsible for the aforementioned record T c. In this work, we use angle-resolved photoemission spectroscopy (ARPES) to investigate the inherent electronic structure of the NdFeAsO 0.6 F 0.4 compound with a twice higher T c = 38 K. We find a similarly singular Fermi surface and further demonstrate that the dramatic enhancement of superconductivity in this compound correlates closely with the fine-tuning of one of the band-edge singularities to within a fraction of the superconducting energy gap Δ below the Fermi level. Our results provide compelling evidence that the band-structure singularities near the Fermi level in the iron-based superconductors must be explicitly accounted for in any attempt to understand the mechanism of superconducting pairing in these materials.
Multiple bands: A key to high-temperature superconductivity in iron arsenides?
JETP Letters, 2009
In the framework of four-band model of superconductivity in iron arsenides proposed by Barzykin and Gor'kov we analyze the gap ratios on hole -like and electron -like Fermi -surface cylinders. It is shown that experimentally observed (ARPES) gap ratios can be obtained only within rather strict limits on the values of pairing coupling constants. The difference of Tc values in 1111 and 122 systems is reasonably explained by the relative values of partial densities of states. The multiple bands electronic structure of these systems leads to a significant enhancement of effective pairing coupling constant determining Tc, so that high enough Tc values can be achieved even for the case of rather small intraband and interband pairing interactions.