Phonon density of states in<mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" display="inline"><mml:mrow><mml:msub><mml:mrow><mml:mtext>NdFeAsO</mml:mtext></mml:mrow><mml:mrow><mml:mn>1</mml:mn><mml:mo>−</mml:mo><mml:mi>x</mml:mi></mml:mrow></mml:msub><mml:msub><mml:mtext>F</mml:mtext><mml:mi>x</mml:mi></mml:msub></mml:mrow></mml:math>

Tacon, M. Le; Krisch, M.; Bosak, A.; Bos, J.-W. G.; Margadonna, Serena

doi:10.1103/physrevb.78.140505

Cited by 46 publications

(50 citation statements)

References 16 publications

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“…35 single crystals indicate that specific phonon modes are strongly renormalized upon fluorine doping [16]. Inelastic X-ray scattering measurements [17] on polycrystalline NdFeAsO 1−y F y samples also revealed softening in the phonon density of states under F doping. The role of spin-phonon coupling has also been investigated experimentally by Raman scattering.…”

Section: Introductionmentioning

confidence: 92%

Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

Zbiri

Mittal

Rols

et al. 2010

J. Phys.: Condens. Matter

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Abstract. To shed light on the role of magnetism on the superconducting mechanism of the oxygen-free FeAs pnictides, we investigate the effect of magnetic ordering on phonon dynamics in the low-temperature orthorhombic parent compounds, which present a spin-density wave. The study covers both the 122 (AFe 2 As 2 ; A=Ca, Sr, Ba) and 1111 (AFeAsF; A=Ca, Sr) phases. We extend our recent work on the Ca (122 and 1111) and Ba (122) cases by treating computationally and experimentally the 122 and 1111 Sr compounds. The effect of magnetic ordering is investigated through detailed non-magnetic and magnetic lattice dynamical calculations. The comparison of the experimental and calculated phonon spectra shows that the magnetic interactions/ordering have to be included in order to reproduce well the measured density of states. This highlights a spin-correlated phonon behavior which is more pronounced than the apparently weak electron-phonon coupling estimated in these materials. Furthermore, there is no noticeable difference between phonon spectra of the 122 Ba and Sr, whereas there are substantial differences when comparing these to CaFe 2 As 2 originating from different aspects of structure and bonding.

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Section: Introductionmentioning

confidence: 92%

Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

Zbiri

Mittal

Rols

et al. 2010

J. Phys.: Condens. Matter

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“…Early calculations based on the virtual crystal approximation suggested that doping should induce only minor changes in the phonon spectra. 3 Our previous PDOS data 12 together with the present singlecrystal data demonstrate the failure of such an approach to properly describe the effects of doping. More recently, F doping was explicitly taken into account in a 2 ϫ 2 ϫ 1 supercell within a local-density approximation approach.…”

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confidence: 99%

“…12 In particular, it was found that even at room temperature, at least one of the three phonon branches located around 23 meV softens on doping. All the three modes are polarized out of the ͑Fe,As͒ planes, parallel to the c axis, and involve motions of either the As or Fe ions.…”

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confidence: 99%

Inelastic x-ray scattering study of superconductingSmFeAsO1−xFysingle crystals: Evidence for strong momentum-dependent doping-induced renormalizations of optical phonons

et al. 2009

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We report inelastic x-ray scattering experiments on the lattice dynamics in SmFeAsO and superconducting SmFeAsO 0.60 F 0.35 single crystals. Particular attention was paid to the dispersions along the ͓100͔ direction of three optical modes close to 23 meV, polarized out of the FeAs planes. Remarkably, two of these modes are strongly renormalized upon fluorine doping. These results provide significant insight into the energy and momentum dependence of the coupling of the lattice to the electron system and underline the importance of spin-phonon coupling in the superconducting iron pnictides. DOI: 10.1103/PhysRevB.80.220504 PACS number͑s͒: 74.25.Kc, 63.20.Ϫe, 74.25.Gz, 78.70.Ck The recent discovery of superconductivity in FeAs-based compounds has stimulated considerable interest. 1 To date three distinct families of FeAs-based superconductors with respective formulas XFeAs ͑X =Li or Na͒, MFe 2 As 2 ͑M =Ca,Ba,Sr͒, and REFeAsO ͑where RE is a rare-earth metal͒-the so-called "111's," "122's," and "1111's"-have been identified. Among them, the last family has the highest values of the superconducting transition temperature T c : depending on the lanthanide, T c can be as high as 55 K. 2 The high value of T c and early DFT calculations 3 initially appeared to support the notion of an exotic mechanism for superconductivity in these materials. However, recent experiments have established that the role of phonons in the electron coupling cannot be totally ignored. In particular, the observation of large Fe isotope effects 4 and the fact that the Fe-As configuration is intimately related to T c ͑Ref. 5͒ and to the magnetic state of the iron sublattice 6,7 show that the lattice is actively involved in this problem. In addition, substantial deviations have been found between the experimentally observed phonon density of states ͑PDOS͒ and ab initio calculations, 8 suggesting that these calculations do not capture all the relevant physics. A spin-polarized calculation is, for example, required to obtain good agreement with the experimental phonon dispersion in the case of undoped CaFe 2 As 2 , even above the magnetic ordering temperature T N . 9 Furthermore, it was recently demonstrated that zonecenter Raman active phonons are strongly renormalized at T N in Ba 1−x K x Fe 2 As 2 ͑Ref. 10͒ and Ba͑Fe 1−x Co x ͒ 2 As 2 . 11 These results all highlight the role of spin-phonon coupling in iron pnictides.In previous experiments on NdFeAsO 1−x F x powders, an unexpected signature of the doping in the PDOS was discovered. 12 In particular, it was found that even at room temperature, at least one of the three phonon branches located around 23 meV softens on doping. All the three modes are polarized out of the ͑Fe,As͒ planes, parallel to the c axis, and involve motions of either the As or Fe ions. At least one of the modes couples directly to the magnetic iron sublattice. 7,13 Here, we utilize inelastic x-ray scattering ͑IXS͒ to investigate the phonon dispersions of SmFeAsO and superconducting SmFeAsO 0.60 F 0.35 single crystals, with...

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“…NdCoAsO is an itinerant ferromagnet ͑T C =85 K͒ that shows a transition to long-range AF order ͑T N =9 K͒ upon ordering of the rare-earth spins. This work follows on from our earlier investigations into the effects of electron ͑via F substitution͒ 20,27 and hole doping ͑via Ca and Sr substitution͒ 28,29 of the parent material NdFeAsO. 4 , and Co powders of at least 99.9% purity were mixed using mortar and pestle and pressed into pellets.…”

Section: Introductionmentioning

confidence: 99%

Superconductivity inNdFe1−xCoxAsO(

et al. 2010

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The phase diagram of NdFe 1−x Co x AsO for low cobalt substitution consists of a superconducting dome ͑0.05Ͻ x Ͻ 0.20͒ with a maximum critical temperature of 16.5͑2͒ K for x = 0.12. The x = 1 end member, NdCoAsO, is an itinerant ferromagnet ͑T C =85 K͒ with an ordered moment of 0.30͑1͒ B at 15 K. Below T N = 9 K, Nd spin ordering results in the antiferromagnetic coupling of the existing ferromagnetic planes. Rietveld analysis reveals that the electronically important twofold tetrahedral angle increases from 111.4°to 115.7°in this series. Underdoped samples with x = 0.046͑2͒ and x = 0.065͑2͒ show distortions to the orthorhombic Cmma structure at 72͑2͒ and 64͑2͒ K, respectively. The temperature dependences of the critical fields H c2 ͑T͒ near T c are linear with almost identical slopes of 2.3͑1͒ T K −1 for x = 0.065͑2͒, x = 0.118͑2͒, and x = 0.172͑2͒. The estimated critical field H c2 ͑0͒ and correlation length for optimally doped samples are 26͑1͒ T and 36͑1͒ Å. A comparison of the maximum reported critical temperatures of well-characterized cobalt-doped 122-and 1111-type superconductors is presented.

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Phonon density of states inNdFeAsO1−xFx

Cited by 46 publications

References 16 publications

Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

Magnetic lattice dynamics of the oxygen-free FeAs pnictides: how sensitive are phonons to magnetic ordering?

Inelastic x-ray scattering study of superconductingSmFeAsO1−xFysingle crystals: Evidence for strong momentum-dependent doping-induced renormalizations of optical phonons

Superconductivity inNdFe1−xCoxAsO(

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