Electronic structure of detwinned BaFe<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>As<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow /><mml:mrow><mml:mn>2</mml:mn></mml:mrow></mml:msub></mml:mrow></mml:math>from photoemission and first principles

Kim, Yeongkwan; Oh, Hyungju; Kim, Chul; Song, Dongjoon; Jung, Wooyong; Kim, Beomyoung; Choi, Hyoung Joon; Kim, Changyoung; Lee, Bumsung; Khim, Seunghyun; Kim, Hyeonwoo; Kim, Kee Hoon; Hong, Jisook; Kwon, Young Sam

doi:10.1103/physrevb.83.064509

Cited by 69 publications

(83 citation statements)

References 29 publications

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“…This orbital differentiation signals that the material is in the vicinity of an orbital selective Mott transition, as proposed previously for other iron pnictides [14], where xy orbital is effectively insulating while other orbitals remain metallic. In Fig.1(b) we also display mass enhancement extracted from optics [15][16][17][18] and ARPES [19][20][21][22][23][24] measurements, and notice a good agreement between our theory and experiment when available. The effective mass extracted from ARPES and optics should be compared with that of the t2g orbitals which contribute most of the spectral weight at low energy.…”

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confidence: 90%

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

2011

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The iron pnictide and chalcogenide compounds are a subject of intensive investigations due to their high temperature superconductivity.[1] They all share the same structure, but there is significant variation in their physical properties, such as magnetic ordered moments, effective masses, superconducting gaps and T c . Many theoretical techniques have been applied to individual compounds but no consistent description of the trends is available [2]. We carry out a comparative theoretical study of a large number of iron-based compounds in both their magnetic and paramagnetic states. We show that the nature of both states is well described by our method and the trends in all the calculated physical properties such as the ordered moments, effective masses and Fermi surfaces are in good agreement with experiments across the compounds. The variation of these properties can be traced to variations in the key structural parameters, rather than changes in the screening of the Coulomb interactions. Our results provide a natural explanation of the strongly Fermi surface dependent superconducting gaps observed in experiments [3]. We propose a specific optimization of the crystal structure to look for higher T c superconductors.The iron pnictides are Hund's metals [4], where the interaction between the electrons is not strong enough to fully localize them, but it significantly slows them down, so that the low energy quasiparticles have much enhanced mass. These quasiparticles are composites of charge and a fluctuating magnetic moment originating in the Hund's rule interactions which tend to align electrons with the same spin and different orbital quantum numbers when they find themselves on the same iron atom.A central puzzle in this field is posed by the variation of the ordered magnetic moment across the iron pnictides/chalcogenides series. In the fully localized picture the atom resides in a single valence, therefore the ordered moment is equal to the atomic moment (4µ B per iron), possibly reduced by quantum fluctuations. This picture is realized in cuprate superconductors where quantum fluctuations reduce the Cu 2+ moment by 20%. In the fully itinerant weak coupling picture, such as spin density wave (SDW) in chromium metal, the ordered moment is related to the degree of Fermi surface nesting. It is by now clear that the iron pnictides are not well described by either fully localized or fully itinerant picture, nor by the density functional theory (DFT), which greatly overestimates the ordered magnetic moments. It has been advocated that the shortcomings of DFT can be circumvented by incorporating the physics of long wavelength fluctuations [5]. Here we take the opposite perspective. While critical long-wavelength fluctuations certainly play a role near the phase transition lines, we will show that the local fluctuations on the iron atom can account for the correct trend of magnetic moments and correlation strength in iron pnictides/chalcogenide layered compounds.Using the combination of density functional theory and d...

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Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

2011

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“…A Dirac cone characterized by a degeneracy point in the linear band dispersion is known to be realized in materials with special geometrical symmetries, such as the K-K' degenerate points in graphene [1], topological insulators (TIs) with the Z 2 symmetrical constraint [2], some organic conductors [3] with a degenerate crossing band, and iron pnictides with different d xy -d xz orbital symmetry [4][5][6][7][8][9][10][11][12][13][14][15][16]. One of the significant features of electronic transport in the Dirac cone states is the large suppression of backward scattering as a consequence of the Berry's phase.…”

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confidence: 99%

Suppression of backward scattering of Dirac fermions in iron pnictides Ba(Fe1−xRuxAs)
Tanabe¹,
Huynh²,
Urata³
et al. 2012
Phys. Rev. B
14
2
18
0
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We report electronic transport of Dirac cones when Fe is replaced by Ru, which has an isoelectronic electron configuration to Fe, using single crystals of Ba(Fe1−xRuxAs)2. The electronic transport of parabolic bands is shown to be suppressed by scattering due to the crystal lattice distortion and the impurity effect of Ru, while that of the Dirac cone is not significantly reduced due to the intrinsic character of Dirac cones. It is clearly shown from magnetoresistance and Hall coefficient measurements that the inverse of average mobility, proportional to cyclotron effective mass, develops as the square root of the carrier number (n) of the Dirac cones. This is the unique character of the Dirac cone linear dispersion relationship. Scattering of Ru on the Dirac cones is discussed in terms of the estimated mean free path using experimental parameters.

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“…spontaneous breaking of discrete rotational symmetry while preserving translational symmetry, appear in many cases among the Fe-based materials [1,2]. These anisotropies, detected by STM [3], transport (on detwinned samples) [4][5][6], ARPES [7][8][9][10], neutron scattering [11], optical [12] and Raman [13] spectroscopy, and torque magnetometry [14], have largely been interpreted in terms of an intrinsic tendency of these systems to break C 4 symmetry globally due to nematic correlations, due either to spin nematic effects [1,2] or orbital ordering. [15][16][17][18] However, there are also indications of local defect states which break C 4 symmetry [19][20][21][22][23][24].…”

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Origin of electronic dimers in the spin-density wave phase of Fe-based superconductors

2014

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We investigate the emergent impurity-induced states arising from point-like scatterers in the spin-density wave phase of iron-based superconductors within a microscopic five-band model. Independent of the details of the band-structure and disorder potential, it is shown how stable magnetic (π, π) unidirectional nematogens are formed locally by the impurities. Interestingly, these nematogens exhibit a dimer structure in the electronic density, are directed along the antiferromagnetic a-axis, and have typical lengths of ∼ 10 lattice constants in excellent agreement with recent scanning tunnelling experiments. These electronic dimers provide a natural explanation of the dopant-induced transport anisotropy found e.g. in the 122 iron pnictides. [19][20][21][22][23][24]. Since impurities are known to nucleate magnetic order locally [25][26][27], it is reasonable to assume that incipient nematic order in a fluctuating state can be similarly condensed around a defect, to create a local nematic electronic state. Once present, such anisotropic defect structures can influence macroscopic anisotropy as well, and it has been suggested [3,23,28,29] that they are responsible for the resistivity anisotropy observed in detwinned Ba-122 crystals [5,6,29].Because impurities represent a well-defined perturbation which can be examined locally, studying the electronic states they create can yield important information on the background correlations present in the pure system [25]. In YBCO, for example, magnetic droplets formed around Zn impurities are known to have a size consistent with the pure antiferromagnetic (AF) correlation length.[25] At present, the microscopic mechanism responsible for the creation of local defect states in Febased materials and for breaking of rotational symmetry is unclear. Some clues are offered by STM experiments on defects in the underdoped, magnetically ordered phase, where the symmetry is already broken by the (π, 0) spindensity wave (SDW) order (the wave vector is given in the effective 1-Fe Brillouin zone). Fourier transform scanning tunneling spectroscopy (STS) deduced the existence of electronic defects with C 2 symmetry[3] nucleated by the Co dopants in Ca(Fe 1−x Co x ) 2 As 2 , while a more detailed analysis reported a dimer structure.[23] These dimers are approximately eight lattice constants (a) long and oriented along the AF a-axis, consistent with the larger resistivity found along the ferromagnetic b-axis.As a first step in understanding the origin of local C 4 symmetry breaking observed in several experiments on various materials, it seems useful to study a situation where a known chemical impurity substitutes at a known position, and ask why such a dimer-like structure (with charge or local density of states (LDOS) peaks located such a great distance from the impurity site) should be induced. As in the cuprates, this problem should be accessible to weak-coupling theories of these systems, provided they account for the electronic states of the system to which the impurity couples and tre...

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Electronic structure of detwinned BaFe2As2from photoemission and first principles

Cited by 69 publications

References 29 publications

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

Suppression of backward scattering of Dirac fermions in iron pnictides Ba(Fe1−xRuxAs)
Tanabe¹,
Huynh²,
Urata³
et al. 2012
Phys. Rev. B
14
2
18
0
View full text Add to dashboard Cite

Origin of electronic dimers in the spin-density wave phase of Fe-based superconductors

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Electronic structure of detwinned BaFe2As2from photoemission and first principles

Cited by 69 publications

References 29 publications

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

Kinetic frustration and the nature of the magnetic and paramagnetic states in iron pnictides and iron chalcogenides

Suppression of backward scattering of Dirac fermions in iron pnictides Ba(Fe1−xRuxAs)Tanabe1, Huynh2, Urata3 et al. 2012Phys. Rev. B142180View full textAdd to dashboardCite

Origin of electronic dimers in the spin-density wave phase of Fe-based superconductors

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Suppression of backward scattering of Dirac fermions in iron pnictides Ba(Fe1−xRuxAs)
Tanabe¹,
Huynh²,
Urata³
et al. 2012
Phys. Rev. B
14
2
18
0
View full text Add to dashboard Cite