Magnetic order in orbital models of the iron pnictides

Brydon, P. M. R.; Daghofer, Maria; Timm, Carsten

doi:10.1088/0953-8984/23/24/246001

Cited by 29 publications

(42 citation statements)

References 107 publications

(371 reference statements)

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“…The leading instability of the system upon decreasing T is into a state with φ * corresponding to the maximum of the left-hand side of Eq. (23). A simple analysis shows that the maximum is at φ * = 0 for α ≥ 2 and at a finite φ * for 1 < α < 2 (see Fig.…”

Section: The Case D =mentioning

confidence: 91%

“…Orbital Order ARPES measurements on detwinned samples have found that the onset of resistivity anisotropy is accompanied by the onset of orbital order in the paramagnetic phase, with different occupations for the d xz and d yz orbitals 10 . One possibility, explored by several authors in different contexts, is that this orbital ordering is an intrinsic instability of the system [18][19][20][21][22][23][24]26,27 . In line with the theme of this work, we explore another possibility, namely that the orbital order is induced by the Ising-nematic order.…”

Section: Consequences Of the Ising-nematic Ordermentioning

confidence: 99%

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Preemptive nematic order, pseudogap, and orbital order in the iron pnictides

et al. 2012

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Starting from a microscopic itinerant model, we derive and analyze the effective low-energy model for collective magnetic excitations in the iron pnictides. We show that the stripe magnetic order is generally preempted by an Ising-nematic order which breaks C4 lattice symmetry but preserves O(3) spin-rotational symmetry. This leads to a rich phase diagram as function of doping, pressure, and elastic moduli, displaying split magnetic and nematic tri-critical points. The nematic transition may instantly bring the system to the verge of a magnetic transition, or it may occur first, being followed by a magnetic transition at a lower temperature. In the latter case, the preemptive nematic transition is accompanied by either a jump or a rapid increase of the magnetic correlation length, triggering a pseudogap behavior associated with magnetic precursors. Furthermore, due to the distinct orbital character of each Fermi pocket, the nematic transition also induces orbital order. We compare our results to various experiments, showing that they correctly address the changes in the character of the magneto-structural transition across the phase diagrams of different compounds, as well as the relationship between the orthorhombic and magnetic order parameters.

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Section: The Case D =mentioning

confidence: 91%

Section: Consequences Of the Ising-nematic Ordermentioning

confidence: 99%

Preemptive nematic order, pseudogap, and orbital order in the iron pnictides

et al. 2012

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“…23 The FSs of the two-and three-orbital models in the AFM state at half filling are shown in Fig. 1.…”

Section: Modelmentioning

confidence: 99%

Coexistence of Antiferromagnetism and Superconductivity in Iron-Based Superconductors

2014

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We theoretically investigate the coexistence of antiferromagnetism and superconductivity in the iron-based superconductors by using the mean-field theory for two-and three-orbital models. We find that both the s+−-wave and s++-wave superconductivity can coexist with antiferromagnetism in the two models. On Dirac Fermi surfaces emerging in the antiferromagnetic phase, a superconducting-gap function has a node for s++ wave but is nodeless for s+− wave. On the other hand, the gap function on non-Dirac Fermi surfaces is either nodeless or accidentally nodal, depending on the parameters of pairing interaction, which is independent of pairing symmetry. IntroductionUnderstanding the phase diagram of iron-based superconductors is a key to clarify the physics of superconductivity of these systems. Parent compounds of iron-based superconductors show an antiferromagnetic (AFM) spin density wave (SDW) below a Néel temperature. With hole or electron doping, magnetization is suppressed and superconductivity emerges. A close relationship of AFM and superconducting (SC) phases indicates that the formation of a Cooper pair is mediated by spin fluctuation, which leads to s +− -wave order 1, 2 where the sign of the gap function on hole Fermi surfaces (FSs) centered at the momentum k = (0, 0) is opposite to that on electron FSs at k=(π,0) and (0,π). On the other hand, it has been proposed that s ++ -wave order, where the two signs are the same, emerges when orbital fluctuation is responsible for superconductivity. 3, 4 s +− and s ++ are possible candidates of SC symmetry in iron-based superconductors.Since the AFM and SC phases are next to each other, the boundary of the two phases may provide useful information on superconductivity of iron-based superconductors. Intriguingly, Ba 1−x K x Fe 2 As 2 , Ba(Fe 1−x Co x ) 2 As 2 and BaFe 2 (As 1−x P x ) 2 show a microscopically coexisting phase of AFM and SC orders, supported by neutron diffraction, 5, 6 X-ray diffraction, 5, 7-9 and NMR 10, 11 experiments.Such a coexistence phase has theoretically been investigated, 12-17 where it is commonly assumed that FSs in a paramagnetic phase consists of a near-circular hole pocket centered at k = (0, 0) and an elliptical electron pocket at k=(π,0) and (0,π). The AFM order with wave vector Q=(π,0) mixes the hole and electron dispersions and a SDW gap is open. Resulting reconstructed FS is completely different from the FS of original paramagnetic phase. In the coexistence phase, it has been pointed out that the SC-gap function on the newly reconstructed

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“…Another alternative explanation was given by or-bital ordering. [32][33][34][35][36][37][38][39][40][41][42][43][44] In this scenario, the interactions between orbitals drive local ordering in orbital occupancy, and resulting in rotational symmetry breaking. However, all of these consequences are similar to our approach.…”

Section: 1229mentioning

confidence: 99%

Possible nematic order driven by magnetic fluctuations in iron pnictides

et al. 2013

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In this paper, instabilities of the isotropic metallic phase in iron pnictides are investigated. The relevant quartic fermionic interaction terms in the model are identified using phase space arguments. Using the functional integral formalism, a Hubbard-Stratonovich transformation is used to decouple these quartic terms. This procedure introduces several bosonic fields which describe the low-energy collective modes of the system. By studying the behavior of these collective modes, a possible instability is found in the forward scattering channel of the isotropic phase driven by magnetic fluctuations. Using mean field analysis, we obtain a static and homogeneous ground state. This ground state is metallic, but the electron Fermi pockets are distorted unequally at different pockets in momentum space. This results in a desirable nematic ordering which breaks the lattice C4 symmetry but preserves translational symmetry and may explain several experimental observations.

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Magnetic order in orbital models of the iron pnictides

Cited by 29 publications

References 107 publications

Preemptive nematic order, pseudogap, and orbital order in the iron pnictides

Preemptive nematic order, pseudogap, and orbital order in the iron pnictides

Coexistence of Antiferromagnetism and Superconductivity in Iron-Based Superconductors

Possible nematic order driven by magnetic fluctuations in iron pnictides

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