Dichotomy between Large Local and Small Ordered Magnetic Moments in Iron-Based Superconductors

Hansmann, P.; Arita, Ryotaro; Toschi, A.; Sakai, Shiro; Sangiovanni, Giorgio; Held, Karsten

doi:10.1103/physrevlett.104.197002

Cited by 130 publications

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“…Also, angleresolved photoemission spectra for doped BaFe 2 As 2 exhibit a depletion of spectral weight near the Fermi level that differs from the superconducting gap. 11 To investigate the influence of Coulomb correlations on the electronic properties of iron pnictides, various groups 2,6,[12][13][14][15][16][17][18][19][20][21] have used dynamical mean-field theory 22 (DMFT) combined with single-particle Hamiltonians derived from densityfunctional theory. These calculations typically revealed moderate to strong effective mass enhancement, in agreement with experimental data.…”

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confidence: 99%

“…Similar quasiparticle spectra have been obtained for a variety of pnictides. 6,[13][14][15][16][17][18][19][20][21]26,27 In principle, integer occupancy n = 6 can also sustain a Mott phase. This phase occurs, however, at much larger Coulomb energies.…”

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confidence: 99%

“…6,[12][13][14][15][16][17][18] In addition, screening processes differ greatly among pnictide compounds, leading to substantial variation in Coulomb and exchange energies. 23 Resonances in Im (ω) and the corresponding pseudogaps in the interacting density of states might appear therefore only in certain 3d orbitals.…”

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High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

Liebsch

2011

Phys. Rev. B

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Hund coupling in the degenerate five-band Hubbard model near n = 6 occupancy is shown to give rise to a significant depletion of spectral weight above the Fermi level. Calculations within dynamical mean-field theory combined with exact diagonalization reveal that this pseudogap is associated with a collective mode in the self-energy caused by spin fluctuations. The pseudogap is remarkably stable over a wide range of Coulomb and exchange energies, but disappears for weak Hund coupling. The implications of this phenomenon for optical spectra of iron pnictides are discussed. Introduction. The discovery of superconductivity in iron pnictides 1 has stimulated intense discussions concerning the role of correlation effects in these compounds. In contrast to high-T c cuprates, which have antiferromagnetic Mott insulators as parent compounds, pnictides are correlated magnetic metals that tend to show significant deviations from Fermi-liquid behavior. Moreover, as a result of the multiband nature of pnictides, the interplay of Coulomb and exchange interactions gives rise to phenomena not found in cuprates. The importance of Hund coupling in pnictides and chalcogenides was recently pointed out in several theoretical 2-6 and experimental studies. [7][8][9] Optical data on paramagnetic LaFePO (Ref. 10) and BaFe 2 As 2 (Refs. 7-9) reveal a high-energy pseudogap not compatible with normal metal behavior. This pseudogap differs fundamentally from the low-energy gap in the antiferromagnetic spin-density wave phase. Also, angleresolved photoemission spectra for doped BaFe 2 As 2 exhibit a depletion of spectral weight near the Fermi level that differs from the superconducting gap. 11 To investigate the influence of Coulomb correlations on the electronic properties of iron pnictides, various groups 2,6,12-21 have used dynamical mean-field theory 22 (DMFT) combined with single-particle Hamiltonians derived from densityfunctional theory. These calculations typically revealed moderate to strong effective mass enhancement, in agreement with experimental data. Correlations were also shown to give rise to nonzero low-energy scattering rates, 13,16,18 indicating bad metallicity. On the other hand, as a result of the complex band structure of pnictides, all five d bands are important, so that the many-body features exhibit a marked orbital dependence. Moreover, the Fe 3d density of states generally shows two main features separated by a deep minimum slightly above the Fermi energy. In view of these multiband characteristics, it is difficult to distinguish genuine many-body features from single-particle properties. For instance, it is presently not clear to what extent pseudogaps in the interacting density of states are induced by Coulomb correlations or band-structure effects.The aim of the present Rapid Communication is to unravel these competing influences. For this purpose we have performed DMFT calculations for a simplified Hamiltonian consisting of five degenerate semielliptical bands. Since the density of states is featureless, corre...

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High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

Liebsch

2011

Phys. Rev. B

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“…Already the first DFT+DMFT calculations allowed for a better understanding of the Mott-Hubbard transition in V 2 O 3 , 22) of δ-Pu, 23) the Ce volume collapse, 22) and magnetism in Fe and Ni. 24) More recently, among others, iron pnictides and their fluctuating magnetic moment, [25][26][27] complex oxide heterostructures, [28][29][30][31][32] nanoscopic structures, 33,34) thermoelectricity, [35][36][37] spin-orbit interactions, 38,39) and electronic entanglement 40) have been addressed.…”

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confidence: 99%

Towards ab initio Calculations with the Dynamical Vertex Approximation

et al. 2018

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While key effects of the many-body problem-such as Kondo and Mott physics-can be understood in terms of onsite correlations, non-local fluctuations of charge, spin, and pairing amplitudes are at the heart of the most fascinating and unresolved phenomena in condensed matter physics. Here, we review recent progress in diagrammatic extensions to dynamical mean-field theory for ab initio materials calculations. We first recapitulate the quantum field theoretical background behind the two-particle vertex. Next we discuss latest algorithmic advances in quantum Monte Carlo simulations for calculating such two-particle quantities using worm sampling and vertex asymptotics, before giving an introduction to the ab initio dynamical vertex approximation (AbinitioDΓA). Finally, we highlight the potential of AbinitioDΓA by detailing results for the prototypical correlated metal SrVO 3 .

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“…The DMFT has become almost standard for treating electronic-correlated systems in the last decade and has been able to explain some of the spectral 16,17 and magnetic properties [18][19][20] of iron-based superconductors. Yin and Kotliar 15 have proved that the dynamical magnetic susceptibility for all momenta and frequency, which requires the determination of the local irreducible vertices at DMFT level, reproduces the result of inelastic neutron scattering experiment in detail.…”

Section: Introductionmentioning

confidence: 99%

Hole-s_± State Induced by Coexisting Ferro- and Antiferromagnetic and Antiferro-orbital Fluctuations in Iron Pnictides

et al. 2016

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The multi-orbital Hubbard model is investigated in order to clarify the electron correlation effects and the superconductivity in the iron-based superconductor. The renormalization effects on the self-energy and the two-particle irreducible vertex function are calculated on the basis of the dynamical mean field theory. We find that the vertex function exhibits a strong renormalization with the significant orbital dependence as compared with the renormalization factor, when the antiferromagnetic and the antiferro-orbital fluctuations are comparably enhanced due to the electron and the hole Fermi surfaces nesting effects. The orbital-dependent vertex function together with the q ∼ 0 nesting between the two-hole Fermi surfaces results in the inter-orbital ferromagnetic fluctuation gradually enhanced which is expected to be observed in LiFeAs. We show that the hole-s±-wave superconductivity with the sign change of the two-hole Fermi surfaces is realized by the enhanced ferromagnetic fluctuation accompanied by the antiferromagnetic fluctuation and the antiferro-orbital fluctuation.

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Dichotomy between Large Local and Small Ordered Magnetic Moments in Iron-Based Superconductors

Cited by 130 publications

References 36 publications

High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

Towards ab initio Calculations with the Dynamical Vertex Approximation

Hole-s_± State Induced by Coexisting Ferro- and Antiferromagnetic and Antiferro-orbital Fluctuations in Iron Pnictides

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Dichotomy between Large Local and Small Ordered Magnetic Moments in Iron-Based Superconductors

Cited by 130 publications

References 36 publications

High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

High-energy pseudogap induced by Hund coupling in a degenerate Hubbard model

Towards ab initio Calculations with the Dynamical Vertex Approximation

Hole-s± State Induced by Coexisting Ferro- and Antiferromagnetic and Antiferro-orbital Fluctuations in Iron Pnictides

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Hole-s_± State Induced by Coexisting Ferro- and Antiferromagnetic and Antiferro-orbital Fluctuations in Iron Pnictides