Spin excitations in the excitonic spin-density-wave state of the iron pnictides

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

doi:10.1103/physrevb.80.174401

Cited by 66 publications

(81 citation statements)

References 72 publications

(122 reference statements)

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“…A more promising starting point for the pnictides is the prediction of ab initio calculations that the nesting between the electron and hole Fermi pockets derived from the Fe 3d orbitals is responsible for the SDW. 26,27 Theoretical work based on this scenario can be divided into two schools of thought: those which argue that only the nesting is important, [28][29][30][31][32][33][34][35][36][37][38][39] and those which also attempt to account for the complicated orbital structure of the Fermi surfaces. The first approach can be dubbed the "excitonic" theory, as it is based upon the excitonic instability of a semimetal proposed in the 1960s.…”

Section: Introductionmentioning

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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Section: Introductionmentioning

confidence: 99%

Magnetic order in orbital models of the iron pnictides

Brydon¹,

Daghofer²,

Timm³

2011

J. Phys.: Condens. Matter

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“…19,20 Likewise, the structural phase transition of the layered chalcogenide Ta 2 NiSe 5 has been attributed to a spin-singlet EI [21][22][23][24] . The spin-density-wave (SDW) state of iron-pnictide superconductors has sometimes been argued to be of the excitonic origin as well [25][26][27][28] . Finally, an EI state was suggested in a t 2g -orbital system with strong spin-orbit coupling 29 .…”

Section: Introductionmentioning

confidence: 99%

Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings

et al. 2015

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We analyze the stability of excitonic ground states in the two-band Hubbard model with additional electron-phonon and Hund's rule couplings using a combination of mean-field and variational cluster approaches. We show that both the interband Coulomb interaction and the electron-phonon interaction will cooperatively stabilize a charge density wave (CDW) state which typifies an "excitonic" CDW if predominantly triggered by the effective interorbital electron-hole attraction or a "phononic" CDW if mostly caused by the coupling to the lattice degrees of freedom. By contrast, the Hund's rule coupling promotes an excitonic spin density wave. We determine the transition between excitonic charge and spin density waves and comment on a fixation of the phase of the excitonic order parameter that would prevent the formation of a superfluid condensate of excitons. The implications for exciton condensation in several material classes with strongly correlated electrons are discussed.

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“…[64][65][66][67][68][69][70][71] In the itinerant model the magnetic scattering is interpreted as particle-hole excitations from the majority spin states to the minority spin states. [60][61][62][63] The magnetic scattering in metallic BaFe 2 As 2 is compared to the hole-doped La 2−x Sr x CuO 4 and electron-doped Nd 2−x Ce x CuO 4 . The electron density dependence in BaFe 2 As 2 is found to be different from the cuprates…”

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confidence: 99%

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

et al. 2012

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Journal of the Physical Society of Japan FULL PAPERSRaman selection rules for electronic and magnetic excitations in BaFe 2 As 2 were theoretically investigated and applied them to the separate detection of the nodal and anti-nodal gap excitations at the spin density wave (SDW) transition and the separate detection of the nearest and the next nearest neighbor exchange interaction energies.Raman spectra are composed of magnetic excitations with gradually decreasing intensity toward far above the SDW transition temperature (T SDW ) and electronic excitations induced by the Brillouin zone folding below T SDW . The SDW gap has Dirac nodes, be- and change into the gap structure by the first order transition at T SDW , while those from the nodal region gradually change into the SDW state. Magnetic excitations are observed as a very broad peak in all polarization configurations. The selection rule for two-magnon scattering from the stripe spin structure was obtained. Applying it to the two-magnon Raman spectra it is found that the magnetic exchange interaction energies are not presented by the short-range superexchange model, but the second derivative of the total energy of the stripe spin structure with respect to the moment directions.The selection rule and the peak energy are expressed by the two-magnon scattering process in an insulator, but the large spectral weight above twice the maximum spin wave energy is difficult to explain by the decayed spin wave. It may be explained by the electronic scattering of itinerant carriers with the magnetic self-energy in the localized spin picture or the particle-hole excitation model in the itinerant spin picture.The magnetic scattering spectra are compared to the insulating and metallic cuprate superconductors whose spins are believed to be localized.

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Spin excitations in the excitonic spin-density-wave state of the iron pnictides

Cited by 66 publications

References 72 publications

Magnetic order in orbital models of the iron pnictides

Magnetic order in orbital models of the iron pnictides

Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

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Spin excitations in the excitonic spin-density-wave state of the iron pnictides

Cited by 66 publications

References 72 publications

Magnetic order in orbital models of the iron pnictides

Magnetic order in orbital models of the iron pnictides

Competition between excitonic charge and spin density waves: Influence of electron-phonon and Hund's rule couplings

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe2As2

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Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂