Orbitally and magnetically induced anisotropy in iron-based superconductors

Lv, Weicheng; Phillips, Philip

doi:10.1103/physrevb.84.174512

Cited by 86 publications

(99 citation statements)

References 65 publications

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“…Note that these results are insensitive to the microscopic mechanism behind the tetragonal symmetry breaking, i.e. whether it arises due to orbital [28][29][30][31][32][33][34][35] or spin fluctuations 2,36-40 , or electron-phonon coupling. In making quantitative comparison with experiments, an important issue is the presence of twin domains, i.e.…”

Section: Comparison To First-principle Calculations and Arpes Exmentioning

confidence: 99%

Distinguishing spin-orbit coupling and nematic order in the electronic spectrum of iron-based superconductors

Fernandes

Vafek

2014

Phys. Rev. B

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The low-energy electronic states of the iron-based superconductors are strongly affected by both spin-orbit coupling and, when present, by the nematic order. These two effects have different physical origins, yet they can lead to similar gap features in the electronic spectrum. Here we show how to disentangle them experimentally in the iron superconductors with one Fe plane per unit cell. Although the splitting of the low energy doublet at the Brillouin zone center (Γ-point) can be due to either the spin-orbit coupling or the nematic order, or both, the degeneracy of each of the doublet states at the zone corner (M -point) is protected by the space group symmetry even when spin-orbit coupling is taken into account. Therefore, any splitting at M must be due to lowering of the crystal symmetry, such as due to the nematic order. We further analyze a microscopic tight-binding model with two different contributions to the nematic order: dxz/dyz onsite energy anisotropy and the dxy hopping anisotropy. We find that a precise determination of the former, which has been widely used to characterize the nematic phase, requires a simultaneous measurement of the splittings of the Γ-point doublet and at the two low-energy M -point doublets. We also discuss the impact of twin domains and show how our results shed new light on ARPES measurements in the normal state of these materials.

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Section: Comparison To First-principle Calculations and Arpes Exmentioning

confidence: 99%

Distinguishing spin-orbit coupling and nematic order in the electronic spectrum of iron-based superconductors

Fernandes

Vafek

2014

Phys. Rev. B

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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].…”

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confidence: 99%

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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“…Recent bulk transport and scattering measurements have suggested that the nematic phase is driven by electronic, rather than lattice, degrees of freedom [4][5][6][7][8] and is observed in all electronic channels -charge 9,10 , orbital 4 , and spin 7,11 . Spin order and spin fluctuations [12][13][14][15][16] (which couple quadratically to nematicity) as well as orbital order 17,18 and orbital fluctuations 19 (which can couple linearly) have been invoked to explain the nematicity.However, the dominant interaction responsible for the nematic ordering and fluctuations remains 2 unknown and identifying it is a key experimental goal. In this paper, we use variable temperature scanning tunneling spectroscopy to provide new insights into this issue by showing that our spectroscopic signals reveal that nematicity occurs in conjuction with strong antiferroic fluctuations and that both phenomena persist up to temperatures much greater than the temperatures at which longrange order is established.…”

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Visualization of electron nematicity and unidirectional antiferroic fluctuations at high temperatures in NaFeAs

et al. 2014

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Abstract:The driving forces behind electronic nematicity in the iron pnictides remain hotly debated. We use atomic-resolution variable-temperature scanning tunneling spectroscopy to provide the first direct visual evidence that local electronic nematicity and unidirectional antiferroic (stripe) fluctuations persist to temperatures almost twice the nominal structural ordering temperature in the parent pnictide NaFeAs. Low-temperature spectroscopic imaging of nematically-ordered NaFeAs shows anisotropic electronic features that are not observed for isostructural, non-nematic LiFeAs. The local electronic features are shown to arise from scattering interference around crystalline defects in NaFeAs, and their spatial anisotropy is a direct consequence of the structural and stripe-magnetic order present at low temperature. We show that the anisotropic features persist up to high temperatures in the nominally tetragonal phase of the crystal. The spatial distribution and energy dependence of the anisotropy at high temperatures is explained by the persistence of large amplitude, short-range, unidirectional, antiferroic (stripe) fluctuations, indicating that strong density wave fluctuations exist and couple to near-Fermi surface electrons even far from the structural and density wave phase boundaries. Main Text:The nature of the normal state from which superconductivity emerges in unconventional superconductors remains a mystery. It is suspected that electronic interactions present in the normal state play a key role in the formation of the superconducting state 1 . In both the cuprates and the pnictide phase diagrams, magnetically ordered states exist in proximity to the superconducting state, and the pnictides additionally exhibit orbital ordering 2,3 . A crucial additional feature of the pnictides is the appearance of a "nematic'' phase in which the tetragonal rotational symmetry of the ideal pnictide lattice is spontaneously broken below a temperature T S . Recent bulk transport and scattering measurements have suggested that the nematic phase is driven by electronic, rather than lattice, degrees of freedom [4][5][6][7][8] and is observed in all electronic channels -charge 9,10 , orbital 4 , and spin 7,11 . Spin order and spin fluctuations [12][13][14][15][16] (which couple quadratically to nematicity) as well as orbital order 17,18 and orbital fluctuations 19 (which can couple linearly) have been invoked to explain the nematicity.However, the dominant interaction responsible for the nematic ordering and fluctuations remains 2 unknown and identifying it is a key experimental goal. In this paper, we use variable temperature scanning tunneling spectroscopy to provide new insights into this issue by showing that our spectroscopic signals reveal that nematicity occurs in conjuction with strong antiferroic fluctuations and that both phenomena persist up to temperatures much greater than the temperatures at which longrange order is established.The arsenide superconductors consist of one or more iron-arsenide layers with the...

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Orbitally and magnetically induced anisotropy in iron-based superconductors

Cited by 86 publications

References 65 publications

Distinguishing spin-orbit coupling and nematic order in the electronic spectrum of iron-based superconductors

Distinguishing spin-orbit coupling and nematic order in the electronic spectrum of iron-based superconductors

Origin of the Resistivity Anisotropy in the Nematic Phase of FeSe

Visualization of electron nematicity and unidirectional antiferroic fluctuations at high temperatures in NaFeAs

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