Emergent Defect States as a Source of Resistivity Anisotropy in the Nematic Phase of Iron Pnictides

Gastiasoro, Maria N.; Paul, I.; Wang, Yeqing; Hirschfeld, P. J.; Andersen, Brian M.

doi:10.1103/physrevlett.113.127001

Cited by 60 publications

(69 citation statements)

References 41 publications

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“…A recent effective model sensitive to the orbital degree of freedom finds that spin fluctuations generate orbital splitting [75]. The possible role of impurities is also under investigation [48,53,58,[76][77][78][79]. Importantly, orbital or spin fluctuations are also likely candidates for the superconducting pairing glue: magnetic fluctuations are believed to mediate s +− -superconductivity [27,80], and orbital fluctuations are thought to lead to s ++ -superconductivity [74,81].…”

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confidence: 99%

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: Fig 1: (Left)mentioning

confidence: 99%

Magnetic interactions in iron superconductors: A review

Bascones

Valenzuela

Calderón

2015

Comptes Rendus. Physique

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“…In a recent elastoresistance study on the FeSe 1−x S x system [9], the nematic signal along the (110) direction is found to be largest at the nematic QCP, which is different from the Co-doped Ba-122 system [3] and our results. Since an obvious difference between FeSe 1−x S x and Ba-122 systems is the lack of AF order in the former, the large thermal critical fluctuations present in the underdoped Ba-122 samples may be attributed to the fluctuations of striped AF order [28][29][30][31], which gives the same rotational symmetry breaking as the nematic order. This is consistent with the suggestion that no AF QCP presents in these materials [12][13][14] and thus the AF order only contributes to thermal fluctuations along the (110) direction.…”

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Nematic Quantum Critical Fluctuations inBaFe2−xNixAs2
Liu
¹
,
Gu
²
,
Zhang
³

et al. 2016
Phys. Rev. Lett.
49
6
75
1
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We have systematically studied the nematic fluctuations in the electron-doped iron-based superconductor BaFe2−xNixAs2 by measuring the in-plane resistance change under uniaxial pressure. While the nematic quantum critical point can be identified through the measurements along the (110) direction as studied previously, quantum and thermal critical fluctuations cannot be distinguished due to similar Curie-Weiss-like behaviors. Here we find that a sizable pressure-dependent resistivity along the (100) direction is present in all doping levels, which is against the simple picture of an Ising-type nematic model. The signal along the (100) direction becomes maximum at optimal doping, suggesting that it is associated with nematic quantum critical fluctuations. Our results indicate that thermal fluctuations from striped antiferromagnetic order dominate the underdoped regime along the (110) direction. We argue that either there is a strong coupling between the quantum critical fluctuations and the fermions, or more exotically, a higher symmetry may be present around optimal doping.PACS numbers: 74.70. Xa, The normal-state electronic states in many iron-based superconductors show strong in-plane anisotropic properties that break the fourfold rotational symmetry of the lattice due to the presence of nematic order [1][2][3][4][5][6][7][8][9]. The nematic order is typically accompanied by a structural transition at T s following an antiferromagnetic (AF) transition at T N ≤ T s , except for FeSe where no AF order is found [10,11]. Both the AF order and the structural transition disappear around the optimal doping level, indicating the presence of magnetic and/or nematic quantum critical points (QCPs). While there is increasing evidence that the magnetic QCP may not exist in many materials [12][13][14][15][16], the nematic QCP has attracted more and more interest since nematic quantum fluctuations may induce an attractive pairing interaction and thus enhance or even lead to superconductivity [17][18][19].So far, the evidence for the nematic QCP is rather limited. It is shown that the nematic order may go through a zero-temperature order-to-disorder quantum phase transition as shown by elastoresistance [3,9], elastic constants [4,5], and Raman scattering [7,8]. The nematic susceptibility shows divergent behavior with the form of (1/T ) γ around optimal doping [3,5,[7][8][9]20]. However, the value of γ is found to be 1, which suggests that the nematic QCP may result in a mean-field scaling. In the underdoped regime, the nematic susceptibility above the thermal transition T s should show Curie-Weiss-like behavior according to the Landau theory of second-order phase transitions. Therefore, quantum nematic fluctuations seem to show no characteristics distinguishable from thermal fluctuations, which is rather strange since one always expects that quantum and thermal fluctuations within the same system give rise to different critical properties.It has been well accepted that the nematic order in iron pnictides is an Ising-type order...

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“…Fermisurface anisotropies arising, for instance, from the ferroorbital order triggered at the nematic transition, affect mostly the Drude weight [11][12][13]. Anisotropic scattering, can be due to elastic processes, such as the development of local magnetic order around an impurity [14,15], or inelastic processes, such as the scattering of electrons by anisotropic magnetic fluctuations [16,17] known to exist below T s [18]. Recent stress-dependent optical reflectivity studies in Co-doped BaFe 2 As 2 point to a dominant effect of the Drude weight [19,20].…”

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Origin of the Resistivity Anisotropy in the Nematic Phase of FeSe

et al. 2016

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The in-plane resistivity anisotropy is studied in strain-detwinned single crystals of FeSe. In contrast to other iron-based superconductors, FeSe does not develop long-range magnetic order below the nematic/structural transition at Ts ≈90 K. This allows for the disentanglement of the contributions to the resistivity anisotropy due to nematic and magnetic orders. Comparing direct transport and elastoresistivity measurements, we extract the intrinsic resistivity anisotropy of strainfree samples. The anisotropy peaks slightly below Ts and decreases to nearly zero on cooling down to the superconducting transition. This behavior is consistent with a scenario in which the in-plane resistivity anisotropy in FeSe is dominated by inelastic scattering by anisotropic spin fluctuations.PACS numbers: 74.70. Xa, 74.25.Ld Electronic nematicity has emerged as a key concept in iron-based superconductors since the observation of inplane resistivity anisotropy in stress-detwinned crystals of Co-doped BaFe 2 As 2 [1, 2]. The fact that the resistivity anisotropy is much larger than what is expected from the small lattice distortion led to the proposal that the tetragonal-to-orthorhombic transition in the iron pnictides is driven not by phonons, but by an electronic nematic phase. Subsequent experiments revealed an intricate dependence of the resistivity anisotropy on doping (a sign change between electron-and hole-doped materials [2-6]), and disorder [7,8], sparking hot debates about its microscopic origins (see Refs. [9 and 10] for reviews).Electronic contributions involved in the in-plane resistivity anisotropy [10] can be separated into the Drude weight and/or of the scattering rate anisotropies. Fermisurface anisotropies arising, for instance, from the ferroorbital order triggered at the nematic transition, affect mostly the Drude weight [11][12][13]. Anisotropic scattering, can be due to elastic processes, such as the development of local magnetic order around an impurity [14,15], or inelastic processes, such as the scattering of electrons by anisotropic magnetic fluctuations [16,17] known to exist below T s [18]. Recent stress-dependent optical reflectivity studies in Co-doped BaFe 2 As 2 point to a dominant effect of the Drude weight [19,20]. However, stripe magnetic order appearing at the magnetic transition severely complicates the analysis. This is because the magnetic state breaks tetragonal symmetry leading to an anisotropic reconstruction of the Fermi surface [7,21] and to the appearance of "Dirac cones" [22], which may dramatically alter the resistivity anisotropy [23]. Disentangling these contributions is fundamental to reveal the origin of the resistivity anisotropy and, consequently, of the nematic state.In this context, the stoichiometric FeSe [24] is an ideal system. It is rather clean (residual resistivity ratios as high as 50 [25]) and its orthorhombic/nematic phase transition at T s ≈ 90 K is not accompanied by a longrange magnetic order [26] eliminating effects of Fermi surface folding.In this Letter we rep...

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Emergent Defect States as a Source of Resistivity Anisotropy in the Nematic Phase of Iron Pnictides

Cited by 60 publications

References 41 publications

Magnetic interactions in iron superconductors: A review

Magnetic interactions in iron superconductors: A review

Nematic Quantum Critical Fluctuations inBaFe2−xNixAs2
Liu
¹
,
Gu
²
,
Zhang
³

et al. 2016
Phys. Rev. Lett.
49
6
75
1
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Origin of the Resistivity Anisotropy in the Nematic Phase of FeSe

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Emergent Defect States as a Source of Resistivity Anisotropy in the Nematic Phase of Iron Pnictides

Cited by 60 publications

References 41 publications

Magnetic interactions in iron superconductors: A review

Magnetic interactions in iron superconductors: A review

Nematic Quantum Critical Fluctuations inBaFe2−xNixAs2Liu1, Gu2, Zhang3 et al. 2016Phys. Rev. Lett.496751View full textAdd to dashboardCite

Origin of the Resistivity Anisotropy in the Nematic Phase of FeSe

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Nematic Quantum Critical Fluctuations inBaFe2−xNixAs2
Liu
¹
,
Gu
²
,
Zhang
³

et al. 2016
Phys. Rev. Lett.
49
6
75
1
View full text Add to dashboard Cite