High-temperature superconductivity in transition metal oxypnictides: A rare-earth puzzle?

Некрасов, И. А.; Pchelkina, Z. V.; Sadovskiǐ, M. V.

doi:10.1134/s002136400810010x

Cited by 68 publications

(77 citation statements)

References 4 publications

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“…[20,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51] While these differ in detail a number of common features are present. Fig.…”

Section: Crystal Structure and Chemistrymentioning

confidence: 92%

Electronic structure of Fe-based superconductors

Singh

2009

Physica C: Superconductivity

140

114

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“…[20,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51] While these differ in detail a number of common features are present. Fig.…”

Section: Crystal Structure and Chemistrymentioning

confidence: 92%

Electronic structure of Fe-based superconductors

Singh

2009

Physica C: Superconductivity

140

114

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“…Models from 2 to 8 orbitals per one-Fe unit cell have been used. Pnictogen and chalcogen orbitals lie several eV below the Fermi level [93] and many models only include their effect in the hopping integrals between Fe-d orbitals. Some authors have used only 2 to 4 orbitals per Fe atom.…”

Section: Models and Techniquesmentioning

confidence: 99%

Magnetic interactions in iron superconductors: A review

Bascones

Valenzuela

Calderón

2015

Comptes Rendus. Physique

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High temperature superconductivity in iron pnictides and chalcogenides emerges when a magnetic phase is suppressed. The multi-orbital character and the strength of correlations underlie this complex phenomenology, involving magnetic softness and anisotropies, with Hund's coupling playing an important role. We review here the different theoretical approaches used to describe the magnetic interactions in these systems. We show that taking into account the orbital degree of freedom allows us to unify in a single phase diagram the main mechanisms proposed to explain the (π, 0) order in iron pnictides: the nesting-driven, the exchange between localized spins, and the Hund induced magnetic state with orbital differentiation. Comparison of theoretical estimates and experimental results helps locate the Fe superconductors in the phase diagram. In addition, orbital physics is crucial to address the magnetic softness, the doping dependent properties, and the anisotropies.

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“…13) Conventional density-functional calculations with the local density approximation (LDA) or the generalized gradient approximation (GGA) have clarified that bands originating from 10-fold degenerate Fe-3d orbitals in a unit cell containing two Fe atoms are close to the Fermi level. The LDA calculations of the 1111-type, [14][15][16][17][18][19][20] 122-type, 21,22) 111-type, 23) and 11-type compounds 24,25) show a very similar band structure for all of the above families, where small electron pockets around M point and hole pockets around À point lead to a semimetallic Fermi surfaces. The local spin density approximation (LSDA) also commonly predicted the antiferromagnetic order for mother materials.…”

Section: Introductionmentioning

confidence: 99%

Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe₂As₂, LiFeAs, FeSe, and FeTe: Electron Correlation and Covalency

et al. 2010

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Effective low-energy Hamiltonians for several different families of iron-based superconductors are compared after deriving them from the downfolding scheme based on first-principles calculations. Systematic dependences of the derived model parameters on the families are elucidated, many of which are understood from the systematic variation of the covalency between Fe-3d and pnictogen-/chalcogenp orbitals. First, LaFePO, LaFeAsO (1111), BaFe 2 As 2 (122), LiFeAs (111), FeSe, and FeTe (11) have overall similar band structures near the Fermi level, where the total widths of 10-fold Fe-3d bands are mostly around 4.5 eV. However, the derived effective models of the 10-fold Fe-3d bands (d model) for FeSe and FeTe have substantially larger effective onsite Coulomb interactions U $ 4:2 and 3.4 eV, respectively, after the screening by electrons on other bands and after averaging over orbitals, as compared to $2:5 eV for LaFeAsO. The difference is similar in the effective models containing p orbitals of As, Se or Te (dp or dpp model), where U ranges from $4 eV for the 1111 family to $7 eV for the 11 family. The exchange interaction J has a similar tendency. The family dependence of models indicates a wide variation ranging from weak correlation regime (LaFePO) to substantially strong correlation regime (FeSe). The origin of the larger effective interaction in the 11 family is ascribed to smaller spread of the Wannier orbitals generating larger bare interaction, and to fewer screening channels by the other bands. This variation is primarily derived from the distance h between the pnictogen/chalcogen position and the Fe layer: The longer h for the 11 family generates more ionic character of the bonding between iron and anion atoms, while the shorter h for the 1111 family leads to more covalent-bonding character, the larger spread of the Wannier orbitals, and more efficient screening by the anion p orbitals. The screened interaction of the d model is strongly orbital dependent, which is also understood from the Wannier spread. The dp and dpp models show much weaker orbital dependence. The larger h also explains why the 10-fold 3d bands for the 11 family are more entangled with the smearing of the ''pseudogap'' structure above the Fermi level seen in the 1111 family. While the family-dependent semimetallic splitting of the bands primarily consists of d yz =d zx and d x 2 Ày 2 orbitals, the size of the pseudogap structure is controlled by the hybridization between these orbitals and d xy =d 3z 2 Àr 2 : A large hybridization in the 1111 family generates a large ''band-insulating''-like pseudogap (hybridization gap), whereas a large h in the 11 family weakens them, resulting in a ''half-filled'' like bands of orbitals. This may enhance strong correlation effects in analogy with Mott physics and causes the orbital selective crossover in the three orbitals. On the other hand, the geometrical frustration t 0 =t, inferred from the ratio of the next-nearest transfer t 0 to the nearest one t of the d model is relatively larger for the...

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High-temperature superconductivity in transition metal oxypnictides: A rare-earth puzzle?

Cited by 68 publications

References 4 publications

Electronic structure of Fe-based superconductors

Electronic structure of Fe-based superconductors

Magnetic interactions in iron superconductors: A review

Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe₂As₂, LiFeAs, FeSe, and FeTe: Electron Correlation and Covalency

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High-temperature superconductivity in transition metal oxypnictides: A rare-earth puzzle?

Cited by 68 publications

References 4 publications

Electronic structure of Fe-based superconductors

Electronic structure of Fe-based superconductors

Magnetic interactions in iron superconductors: A review

Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe2As2, LiFeAs, FeSe, and FeTe: Electron Correlation and Covalency

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Product

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Comparison of Ab initio Low-Energy Models for LaFePO, LaFeAsO, BaFe₂As₂, LiFeAs, FeSe, and FeTe: Electron Correlation and Covalency