Hund’s coupling and its key role in tuning multiorbital correlations

Medici, Luca de’

doi:10.1103/physrevb.83.205112

Cited by 186 publications

(245 citation statements)

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“…However, in the last years it is becoming clear that Hund's coupling plays a key role on the correlations of these materials and other multi-orbital systems [39,42,43,107,110,118,[177][178][179][180][181]. [42,43,[177][178][179][180]. Soon after the discovery of superconductivity in doped LaFeAsO, LDA+DMFT calculations [39,42,100] determined this parent compound to be a correlated metal far from the Mott transition and not well described by either atomic physics or band theory [100].…”

Section: Insight From Ab-initio Calculationsmentioning

confidence: 99%

“…The simplest generalisation of these models allows the coexistence of itinerant weakly correlated orbitals and strongly localised ones. However, in the last years it is becoming clear that Hund's coupling plays a key role on the correlations of these materials and other multi-orbital systems [39,42,43,107,110,118,[177][178][179][180][181]. [42,43,[177][178][179][180].…”

Section: Insight From Ab-initio Calculationsmentioning

confidence: 99%

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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: Insight From Ab-initio Calculationsmentioning

confidence: 99%

Section: Insight From Ab-initio Calculationsmentioning

confidence: 99%

Magnetic interactions in iron superconductors: A review

Bascones

Valenzuela

Calderón

2015

Comptes Rendus. Physique

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“…33 The main difference is that, because of the lower degeneracy, the boundary in Fig. 4 between metallic and insulating phases at half filling is shifted to larger J (except at large U ) 34,35 and that at n = 3 ± 1 the system is relatively farther from the Mott phase than at n = 5 ± 1.…”

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confidence: 99%

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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“…In particular, the central role played by Hund's rule coupling J was recently highlighted, as a theoretical consensus emerged that the electron-electron interaction in multiband materials is dictated by J rather than Coulomb U , or by a nontrivial interplay of both. 1,2 In this context, experimental investigations of electronic excitations are invaluable in exploring the multiband electron dynamics, and scrutinizing the corresponding novel theoretical frameworks. Resonant inelastic x-ray scattering (RIXS) allows such investigations to be carried out in an element-specific and momentumresolved fashion, and in an energy range directly relevant to Coulomb and Hund interactions.…”

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confidence: 99%

“…These results stress the peculiar sensitivity of the RIXS spectrum to the value of J, which reflects the importance of Hund's coupling in the electron correlation of PrFeAsO, consequence of the multiorbital electronic structure of the 1111 pnictide. 1 The orbital composition of the RIXS spectrum can be derived from the calculated diagonal transitions (i.e., for which the initial and final orbital states are identical), and which account for most of the RIXS spectral weight. Such calculations are shown in Fig.…”

mentioning

confidence: 99%