Low Magnetization and Anisotropy in the Antiferromagnetic State of Undoped Iron Pnictides

Bascones, Elena; Calderón, M. J.; Valenzuela, B.

doi:10.1103/physrevlett.104.227201

Cited by 75 publications

(146 citation statements)

References 25 publications

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“…This is consistent with the non-monotonic dependence on doping of the minimal interaction for the onset of magnetism U onset obtained in Hartree-Fock calculations for a five-orbital model [92,107] in which the smallest U onset appears at electronic fillings close to that of undoped compounds n ∼ 6, see Fig. 5(d).…”

Section: A Weak Coupling Description Of Magnetismsupporting

confidence: 75%

“…Techniques used to study these multi-orbital models include: Random Phase Approximation (RPA) [83,103], FLEX [91], momentum and real-space HartreeFock (HF) [37,92,[104][105][106][107][108], Functional Renormalisation Group (FRG) [109], Dynamical Mean Field Theory (DMFT) [39,42,100,[110][111][112][113], Monte Carlo [114], Gutzwiller variational theory [102,[115][116][117] and Slave Spin [40,118,119]. Different techniques approach the model in weakly or strongly correlated limits and can underestimate or overestimate the effect of interactions.…”

Section: Models and Techniquesmentioning

confidence: 99%

“…A different approach deals with lattice multi-orbital systems adding interactions to tight-binding models which mimic the bandstructure close to the Fermi surface [31,37,83,[89][90][91][92]. Models from 2 to 8 orbitals per one-Fe unit cell have been used.…”

Section: Models and Techniquesmentioning

confidence: 99%

See 2 more Smart Citations

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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Section: A Weak Coupling Description Of Magnetismsupporting

confidence: 75%

Section: Models and Techniquesmentioning

confidence: 99%

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Magnetic interactions in iron superconductors: A review

Bascones

Valenzuela

Calderón

2015

Comptes Rendus. Physique

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“…81 Although the existence of superconductivity in these models has been extensively studied, 40,[44][45][46]48,51,53,56,60,63,64,66 the magnetic behaviour remains rather poorly understood. The most popular approach to the appearance of AFM order in these models is to examine the ground state using a standard mean-field ansatz that allows for at most twosite magnetic unit cells; 47,50,52,54,58,59,61,64 very recently, this has been generalized to a Gutzwiller mean-field theory. 65,68 As all of the orbital models have a rather complicated electronic structure, however, it is by no means certain that such phases have the lowest free energy, i.e.…”

Section: Arxiv:10071949v2 [Cond-matsupr-con] 27 May 2011mentioning

confidence: 99%

“…When constructing the mean-field phase diagrams of the orbital models, we adopt the frequently-employed ansatz 54,58,59,61,64,83 B. The magnetic susceptibility…”

Section: A Mean-field Analysismentioning

confidence: 99%

Magnetic order in orbital models of the iron pnictides

Brydon¹,

Daghofer²,

Timm³

2011

J. Phys.: Condens. Matter

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We examine the appearance of the experimentally-observed stripe spin-density-wave magnetic order in five different orbital models of the iron pnictide parent compounds. A restricted meanfield ansatz is used to determine the magnetic phase diagram of each model. Using the random phase approximation, we then check this phase diagram by evaluating the static spin susceptibility in the paramagnetic state close to the mean-field phase boundaries. The momenta for which the susceptibility is peaked indicate in an unbiased way the actual ordering vector of the nearby meanfield state. The dominant orbitally resolved contributions to the spin susceptibility are also examined to determine the origin of the magnetic instability. We find that the observed stripe magnetic order is possible in four of the models, but it is extremely sensitive to the degree of the nesting between the electron and hole Fermi pockets. In the more realistic five-orbital models, this order competes with a strong-coupling incommensurate state which appears to be controlled by details of the electronic structure below the Fermi energy. We conclude by discussing the implications of our work for the origin of the magnetic order in the pnictides.

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On the multi‐orbital band structure and itinerant magnetism of iron‐based superconductors

2011

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This paper explains the multi-orbital band structures and itinerant magnetism of the iron-pnictide and chalcogenide superconductors. We first describe the generic band structure of a single, isolated FeAs layer. Use of its Abelian glide-mirror group allows us to reduce the primitive cell to one FeAs unit. For the lines and points of high symmetry in the corresponding large, square Brillouin zone, we specify how the one-electron Hamiltonian factorizes. From density-functional theory, and for the observed structure of LaOFeAs, we generate the set of eight Fe d and As p localized Wannier functions and their tight-binding (TB) Hamiltonian, h (k). For comparison, we generate the set of five Fe d Wannier orbitals. The topology of the bands, i.e. allowed and avoided crossings, specifically the origin of the d 6 pseudogap, is discussed, and the role of the As p orbitals and the elongation of the FeAs4 tetrahedron emphasized. We then couple the layers, mainly via interlayer hopping between As pz orbitals, and give the formalism for simple tetragonal and body-centered tetragonal (bct) stackings. This allows us to explain the material-specific 3D band structures, in particular the complicated ones of bct BaFe2As2 and CaFe2As2 whose interlayer hoppings are large. Due to the high symmetry, several level inversions take place as functions of kz or pressure, and linear band dispersions (Dirac cones) are found at many places. The underlying symmetry elements are, however, easily broken by phonons or impurities, for instance, so that the Dirac points are not protected. Nor are they pinned to the Fermi level because the Fermi surface has several sheets. From the paramagnetic TB Hamiltonian, we form the band structures for spin spirals with wavevector q by coupling h (k) and h (k + q) . The band structure for stripe order is studied in detail as a function of the exchange potential, ∆, or moment, m, using Stoner theory. Gapping of the Fermi surface (FS) for small ∆ requires matching of FS dimensions (nesting) and d-orbital characters. The interplay between pd hybridization and magnetism is discussed using simple 4 × 4 Hamiltonians. The origin of the propeller-shaped Fermi surface is explained in detail. Finally, we express the magnetic energy as the sum over band-structure energies and this enables us to understand to what extent the magnetic energies might be described by a Heisenberg Hamiltonian, and to address the much discussed interplay between the magnetic moment and the elongation of the FeAs4 tetrahedron.Copyright line will be provided by the publisher ForewordThis paper is dedicated to Manuel Cardona, on the occasion of his 75th birthday. Manuel Cardona is worldfamous not only for being an outstanding and creative experimentalist, but also for having deep theoretical insights, in particular into the band structures of solids. His book [1] with Peter Yu on Fundamentals of Semiconductors, now a classic of solid-state physics, devotes a large part to the explanation of theory in simple, accessible language. For our contribu...

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Low Magnetization and Anisotropy in the Antiferromagnetic State of Undoped Iron Pnictides

Cited by 75 publications

References 25 publications

Magnetic interactions in iron superconductors: A review

Magnetic interactions in iron superconductors: A review

Magnetic order in orbital models of the iron pnictides

On the multi‐orbital band structure and itinerant magnetism of iron‐based superconductors

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