Anisotropic charge dynamics in detwinned Ba(Fe
 1-x
 Co
 x
 )
 2
 As
 2

Dusza, A.; Lucarelli, Andrea; Pfuner, F.; Chu, Jiun‐Haw; Fisher, I. R.; Degiorgi, L.

doi:10.1209/0295-5075/93/37002

Cited by 139 publications

(178 citation statements)

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“…2 A and B shows the temperature evolution of the optical conductivity spectra of detwinned BaFe 2 As 2 (after annealing) over a wide energy range for the a-and b-axis polarizations [σ a ðωÞ and σ b ðωÞ], respectively (see Materials and Methods and SI Text for the details for obtaining the optical conductivity). Both spectra are identical within the present experimental precision at temperatures above 200 K in stark contrast to the result taken by Dusza et al (25). Note that the measurement was carried out under uniaxial pressure even in the tetragonal phase above T s , evidencing that the applied pressure hardly affects the charge dynamics.…”

Section: Figuresupporting

confidence: 85%

“…Optical conductivity [σðωÞ] is the absorptive current response to a time-varying external electric field of frequency ω; hence, it is an extension of the dc (ω ¼ 0) conductivity to finite energies. A similar optical measurement on a detwinned BaFe 2 As 2 crystal has been done also by Dusza et al (25), but the spectral feature in the low-energy data is not clear enough to inquire the connection to the origin of the anisotropy in resisAuthor contributions: M.N., T.I., and S.U. designed research; M.N., T.L., S.I., Y.T., K.K., and C.H.L.…”

supporting

confidence: 61%

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Unprecedented anisotropic metallic state in undoped iron arsenide BaFe ₂ As ₂ revealed by optical spectroscopy

Nakajima

Liang

Ishida

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

191

189

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An ordered phase showing remarkable electronic anisotropy in proximity to the superconducting phase is now a hot issue in the field of high-transition-temperature superconductivity. As in the case of copper oxides, superconductivity in iron arsenides competes or coexists with such an ordered phase. Undoped and underdoped iron arsenides have a magnetostructural ordered phase exhibiting stripe-like antiferromagnetic spin order accompanied by an orthorhombic lattice distortion; both the spin order and lattice distortion break the tetragonal symmetry of crystals of these compounds. In this ordered state, anisotropy of in-plane electrical resistivity is anomalous and difficult to attribute simply to the spin order and/or the lattice distortion. Here, we present the anisotropic optical spectra measured on detwinned BaFe 2 As 2 crystals with light polarization parallel to the Fe planes. Pronounced anisotropy is observed in the spectra, persisting up to an unexpectedly high photon energy of about 2 eV. Such anisotropy arises from an anisotropic energy gap opening below and slightly above the onset of the order. Detailed analysis of the optical spectra reveals an unprecedented electronic state in the ordered phase.anisotropic electronic state | iron pnictide | optical spectrum H igh-transition-temperature (high-T c ) superconductivity realized in both copper oxides and iron arsenides shares common features, namely, the superconducting phase is in close proximity to a symmetry-breaking phase and these phases coexist under certain circumstances, but apparently compete with each other. The close proximity suggests that our understanding of high-T c superconductivity will greatly improve once the nature of this proximate phase is revealed. The parent compounds of iron-arsenide superconductors, with BaFe 2 As 2 as a representative example, are unique metals that undergo a tetragonal-toorthorhombic structural phase transition at temperature T s with a shorter b axis and a longer a axis in the orthorhombic phase always accompanied by antiferromagnetic (AF) spin order at temperature T N . T N is equal to T s in some compounds (1-3) and slightly lower than T s in others (4). BaFe 2 As 2 exhibits stripe-like AF order in which Fe spins align antiferromagnetically in the a-axis direction in the Fe plane and ferromagnetically in the b-axis direction. Anisotropic electronic properties have been experimentally examined by various methods, such as neutron scattering (5), scanning tunneling microscopy (STM) (6), and angleresolved photoemission spectroscopy (ARPES) (7,8). These experiments suggest strong anisotropy of spin excitation and of the shape of Fermi surfaces. However, most of the experiments were performed on twinned crystals with randomly oriented domains, which inhibit the observation of genuine anisotropy.Recently, anisotropic resistivity has been measured on detwinned crystals (9, 10). The anisotropy of resistivity is quite anomalous in that the resistivity along the spin-ferromagnetic (FM) direction with a shorter b axis is...

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Section: Figuresupporting

confidence: 85%

supporting

confidence: 61%

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe ₂ As ₂ revealed by optical spectroscopy

Nakajima

Liang

Ishida

et al. 2011

Proc. Natl. Acad. Sci. U.S.A.

191

189

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“…Optical conductivity measurements concluded that this unexpected anisotropy is caused by changes in the populations of the orbitals d xz and d yz at the Fermi surface (FS). 8 This is in agreement with early mean-field studies where the unbalanced FS orbital population, without long-range orbital order, led to results compatible with photoemission techniques. 9 Several calculations have recently addressed the experimentally observed transport anisotropy.…”

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confidence: 91%

Anisotropy of the optical conductivity of a pnictide superconductor from the undoped three-orbital Hubbard model

Zhang

Dagotto

2011

Phys. Rev. B

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“…Reducing the iron occupancy of the 3d orbital, brings the occupancy of the xy orbital closer to unity, and increases the correlation strength, which in turn strengthens the magnetic moment. This has been observed in ARPES studies of the BaFe 2 As 2 family [28].In the magnetic state, the in-plane resistivity is very anisotropic, as has been shown in optical and transport studies of BaFe 2 As 2 [29,30]. This is a consequence of the strong low energy orbital polarization of the xz and yz orbital [30].…”

supporting

confidence: 54%

“…In the magnetic state, the in-plane resistivity is very anisotropic, as has been shown in optical and transport studies of BaFe 2 As 2 [29,30]. This is a consequence of the strong low energy orbital polarization of the xz and yz orbital [30].…”

mentioning

confidence: 78%

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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Anisotropic charge dynamics in detwinned Ba(Fe _1-x Co _x ) ₂ As ₂

Cited by 139 publications

References 28 publications

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe ₂ As ₂ revealed by optical spectroscopy

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe ₂ As ₂ revealed by optical spectroscopy

Anisotropy of the optical conductivity of a pnictide superconductor from the undoped three-orbital Hubbard model

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

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Anisotropic charge dynamics in detwinned Ba(Fe 1-x Co x ) 2 As 2

Cited by 139 publications

References 28 publications

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe 2 As 2 revealed by optical spectroscopy

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe 2 As 2 revealed by optical spectroscopy

Anisotropy of the optical conductivity of a pnictide superconductor from the undoped three-orbital Hubbard model

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

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Resources

About

Anisotropic charge dynamics in detwinned Ba(Fe _1-x Co _x ) ₂ As ₂

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe ₂ As ₂ revealed by optical spectroscopy

Unprecedented anisotropic metallic state in undoped iron arsenide BaFe ₂ As ₂ revealed by optical spectroscopy