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Chauviere, L.; Gallais, Yann; Cazayous, M.; Méasson, Marie-Aude; Sacuto, A.; Colson, D.; Forget, A.

doi:10.1103/physrevb.82.180521

Cited by 36 publications

(65 citation statements)

References 33 publications

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“…In the (xx) and (ab) spectra the low-energy scattering intensity abruptly increases from 125 K to 130 K in the (xx) spectra and from 120 K to 125 K in the (ab) spectra, and then gradually decreases as temperature increases. 49,50 On the other hand the jump is not observed in the (aa) and (xy) spectra near the T SDW . The small temperature difference of the jump in (xx) and (ab) is induced by the first order transition.…”

Section: Low-energy Spectra Of the Dirac Node And The Anti-nodementioning

confidence: 87%

“…The experimentally obtained B 2g spectra show critical fluctuation just above T SDW and jump into the gap structure at T SDW , while the B 1g spectra gradually change as temperature decreases through the T SDW . 49,50 The gap structure is composed of the reduced intensity below 300 cm −1 and the peaks at 400 and 800 cm −1 . The anti-nodal gap energies are the same as those in infrared spectroscopy 51 and ARPES.…”

Section: -29mentioning

confidence: 99%

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Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

et al. 2012

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Journal of the Physical Society of Japan FULL PAPERSRaman selection rules for electronic and magnetic excitations in BaFe 2 As 2 were theoretically investigated and applied them to the separate detection of the nodal and anti-nodal gap excitations at the spin density wave (SDW) transition and the separate detection of the nearest and the next nearest neighbor exchange interaction energies.Raman spectra are composed of magnetic excitations with gradually decreasing intensity toward far above the SDW transition temperature (T SDW ) and electronic excitations induced by the Brillouin zone folding below T SDW . The SDW gap has Dirac nodes, be- and change into the gap structure by the first order transition at T SDW , while those from the nodal region gradually change into the SDW state. Magnetic excitations are observed as a very broad peak in all polarization configurations. The selection rule for two-magnon scattering from the stripe spin structure was obtained. Applying it to the two-magnon Raman spectra it is found that the magnetic exchange interaction energies are not presented by the short-range superexchange model, but the second derivative of the total energy of the stripe spin structure with respect to the moment directions.The selection rule and the peak energy are expressed by the two-magnon scattering process in an insulator, but the large spectral weight above twice the maximum spin wave energy is difficult to explain by the decayed spin wave. It may be explained by the electronic scattering of itinerant carriers with the magnetic self-energy in the localized spin picture or the particle-hole excitation model in the itinerant spin picture.The magnetic scattering spectra are compared to the insulating and metallic cuprate superconductors whose spins are believed to be localized.

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Section: Low-energy Spectra Of the Dirac Node And The Anti-nodementioning

confidence: 87%

Section: -29mentioning

confidence: 99%

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

et al. 2012

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“…Electronic Raman scattering studies on Ba(Fe1-xCox)2As2 were also performed by L. Chauvière et al 41 They measured B 2g spectra which is similar to those in Ref. 39 and considered the spectra are contributed by excitations around electron-like M pockets.…”

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Raman Scattering in Iron-Based Superconductors

Zhang

2012

Mod. Phys. Lett. B

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Iron-based superconducting layered compounds have the second highest transition temperature after cuprate superconductors.Their discovery is a milestone in the history of high-temperature superconductivity and will have profound implications for high-temperature superconducting mechanism as well as industrial applications. Raman scattering has been extensively applied to correlated electron systems including the new superconductors due to its unique ability to probe multiple primary excitations and their coupling. In this review, we will give a brief summary of the existing Raman experiments in the iron-based materials and their implication for pairing mechanism in particular. And we will also address some open issues from the experiments.Keywords: Raman scattering; iron-based superconductor; electron-phonon coupling; electronic Raman scattering; two-magnon process. BackgroundRaman scattering, also known as inelastic light scattering, was discovered in 1928 by C. V. Raman. It can be used to detect many kinds of excitations in solids, such as phonons, 1 magnons, 2 excitons 3 etc.With the invention of laser and the continuous improvement of monochromator and new-generation detectors, Raman scattering has become a conventional and fundamental technique in many fields.Superconductivity is one of the most important frontiers in condensed matter physics and much Raman scattering work has been done in the field so far. Basically, Raman scattering can probe phonons and related electron-phonon coupling. The information on superconducting gap size can be drawn from cooper-pair-breaking peak in electronic Raman scattering spectra. Symmetry analysis is a unique advantage of Raman scattering. In a non-isotropic superconductor, the position, shape and low-energy behavior of pair-breaking peak will substantially change in different symmetry channels, which gives a unique way to explore pairing symmetry. Raman scattering has also been employed to detect two-magnon procedure in spin-ordered systems, from which we can obtain accurate exchange energies and learn the evolution of spin fluctuation. Actually, Raman scattering plays a crucial role in the study of cuprate superconductors.Since its discovery in 2008, iron-based superconductor has attracted a lot of interests due to its second highest transition temperature after cuprate superconductor. So far, all known iron-based superconductors can be divided into six categories in structure: 1, "1111", represented by F-doped LaFeAsO, is the first iron-based superconductor. The highest Tc reaches up to 56 K by rare-earth substitution. 4 2, "122", represented by Co or K-doped BaFe 2 As 2 , is the most studied system due to available high-quality crystals and tunable doping levels. 5 3, "111" refers to LiFeAs with the maximum Tc of 18 K. 6 4, "11" is Fe(Se,Te), the prototype of iron-based superconductor without poisonous element As. 7 5, "21311" is isostructural to 122 system with a divalent group instead of Ba. 8 6, A 0.8 Fe 1.6 Fe 2 (A=K, Tl, Cs…), which has ordered Fe-vacancies was d...

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“…In A(Fe 1−x Co x ) 2 As 2 (A = Ca, Sr, Ba, Eu) [1,4,19,21,22,24,25], Ba 1−p K p Fe 2 As 2 [25], FeSe [26,27] and NaFe 1−x Co x As [28], a quasi-elastic peak (QEP) with B 2g symmetry (considering the 2 Fe tetragonal cell, see Fig. 1(a)) has been observed and interpreted in terms of either charge/orbital [21,22,24,26,29] or spin [4,25,30,31] nematic fluctuations.…”

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Nematic fluctuations and phase transitions in LaFeAsO: A Raman scattering study

et al. 2017

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Raman scattering experiments on LaFeAsO with splitted antiferromagnetic (TAF M = 140 K) and tetragonal-orthorhombic (TS = 155 K) transitions show a quasi-elastic peak (QEP) in B2g symmetry (2 Fe tetragonal cell) that fades away below ∼ TAF M and is ascribed to electronic nematic fluctuations. A scaling of the reported shear modulus with the T −dependence of the QEP height rather than the QEP area indicates that magnetic degrees of freedom drive the structural transition. The large separation between TS and TAF M in LaFeAsO compared with their coincidence in BaFe2As2 manifests itself in slower dynamics of nematic fluctuations in the former. The discovery of Fe-based superconductors (FeSCs) with high transition temperatures (above 100 K in FeSe films [1]) triggered much interest on these materials [2][3][4][5]. Nematicity, characterized by large in-plane electronic transport anisotropy [6], is normally observed below a tetragonal-orthorhombic transition temperature T S , and seems to be also present in other high-T c superconductors [7]. Also, divergent nematic susceptibility in the optimal doping regime suggests that nematic fluctuations play an important role in the superconducting pairing mechanism [8]. Thus, investigations of the nematic order and fluctuations in FeSCs and their parent materials are pivotal to unraveling the origin of high-T c superconductivity. Clearly, it is necessary to identify the primary order parameter associated with the nematic phase [4, 5]. A relation between nematicity and magnetism is suggested by the near coincidence between T S and the antiferromagnetic (AFM) ordering temperature T AF M in some materials, most notably BaFe 2 As 2 with T AF M ∼ T S = 138 K [9,10]. In fact, the magnetic ground state is a stripe AFM phase that breaks the 4-fold tetragonal symmetry of the lattice (see Fig. 1(a)), providing a natural mechanism for electronic anisotropy. On the other hand, T S and T AF M are significantly separated for LaFeAsO (LFAO) (T AF M = 140 K and T S = 155 K) [11][12][13], while FeSe does not order magnetically at ambient pressure but still shows a nematic transition at T S = 90 K [14], motivating suggestions that the nematic transition may be driven by charge/orbital degrees of freedom rather than magnetism in the latter [16,17]. However, even for FeSe the magnetic scenario may still apply [18]. In * Present address: Materials Science and Technology Division, Oak Ridge National Laboratory, Oak Ridge, Tennessee 37831, USA.Ba(Fe 1−x Co x ) 2 As 2 and other doped systems, the splitting between T AF M and T S increases with doping [9,15]. Overall, the primary order parameter that drives the structural/nematic transition at T S and the dominating mechanism of T AF M /T S separation in parent FeSCs are not fully settled yet.Raman scattering was recently employed as a probe of nematic fluctuations in FeSCs and their parent materials. In A(Fe 1−x Co x ) 2 As 2 (A = Ca, Sr, Ba, Eu) [1, 4,19,21,22,24,25], Ba 1−p K p Fe 2 As 2 [25], FeSe [26,27] and NaFe 1−x Co x As [28], a quasi-elastic ...

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Impact of the spin-density-wave order on the superconducting gap ofBa(Fe1−xCox)

Cited by 36 publications

References 33 publications

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

Raman Scattering in Iron-Based Superconductors

Nematic fluctuations and phase transitions in LaFeAsO: A Raman scattering study

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Impact of the spin-density-wave order on the superconducting gap ofBa(Fe1−xCox)

Cited by 36 publications

References 33 publications

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe2As2

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe2As2

Raman Scattering in Iron-Based Superconductors

Nematic fluctuations and phase transitions in LaFeAsO: A Raman scattering study

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Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂

Spin-Density-Wave Gap with Dirac Nodes and Two-Magnon Raman Scattering in BaFe₂As₂