High pressure studies on Fe-pnictide superconductors

Chu, C. W.; Lorenz, B.

doi:10.1016/j.physc.2009.03.030

Cited by 106 publications

(97 citation statements)

References 74 publications

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“…While in the undoped SmFeAsO there is no appreciable deviation and the two axis are compressed isotropically, the doping induces an internal anisotropic behavior in the pressure range ~1.2 to ~2.7 GPa. This is the same pressure limits where the Fe and As phonons show the anomaly (Fig.3) indicating that the reason of this effect is a doping dependent anisotropic response of the two axis to pressure and more specifically a non-monotonic compression of the superconducting FeAs 4 layer [17], apparently modifying the distribution of the carriers. In addition, our results provide a further indication for the connection of this effect to doping with the data pointing to a local lattice instability very similar to those observed before by high pressure studies in the cuprates [2,3,20].…”

Section: Data Analysis and Discussionmentioning

confidence: 54%

“…Τhe effect of hydrostatic pressure on the transition temperature of these compounds resembles the situation in the high T c cuprates [1,4]. But contrary to the cuprates, there are indications that undoped SmFeAsO becomes superconducting at high pressures [13].…”

Section: Introductionmentioning

confidence: 92%

“…Besides, it can help the study of the superconductivity property and its relation to lattice by modifying the interatomic distances and driving the high T c superconductors towards or away from their lattice instabilities [2,3]. While there is an accumulated amount of data from these studies [1,4], the investigation of high-pressure effects on the Raman spectra is limited. The main reason is the difficulty of studying the very weak modes of the superconducting materials inside the highpressure cell.…”

Section: Introductionmentioning

confidence: 99%

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Non-linear lattice response of Sm oxypnictides to hydrostatic pressure

Liarokapis

Calamiotou

Zhigadlo

et al. 2013

Journal of Physics and Chemistry of Solids

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Hydrostatic pressure Raman measurements have been carried out on the SmFeAsO series of oxypnictides with varying amount of doping (F substitution for O and Co for Fe) and transition temperature (T c ), in order to investigate lattice modifications and their connection to doping and superconductivity. Synchrotron XRD data on some of these compounds indicated that at low doping the lattice constants vary smoothly with pressure, but with increasing F concentration there is a deviation from the normal equation of state and these effects are related with modifications in the superconducting FeAs 4 tetrahedra. The hydrostatic pressure Raman measurements show that the A 1g mode of the rare earth atom for the superconducting compounds deviates from the linear pressure dependence at the same pressures where the XRD results indicate pressure-induced lattice anomalies. A similar anomaly is found for the As phonon of same symmetry. As in cuprates, the effect is diminished in the undoped compounds and it is not related with the F substitution being present in the Sm(Fe 1-x Co x )AsO as well. The calculated Grüneisen parameter for the Sm phonon (γ≈1.5) is very similar to the corresponding values of cuprates and it does not vary with doping. For the Fe mode it has higher value (γ≈1.8) than for As (γ≈1) indicating a more anharmonic phonon.

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Section: Data Analysis and Discussionmentioning

confidence: 54%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

See 1 more Smart Citation

Non-linear lattice response of Sm oxypnictides to hydrostatic pressure

Liarokapis

Calamiotou

Zhigadlo

et al. 2013

Journal of Physics and Chemistry of Solids

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“…37 The resulting basis vectors for the two independent cobalt atoms are given in Table II. The allowed models correspond to an easy-axis ferromagnet ͑⌫ 3 1 ͒, an easy-plane ferromagnet ͑⌫ 9 2 ͒, and two checkerboard antiferromagnets with moments along the c direction ͑⌫ 6 1 ͒ or in the basal plane ͑⌫ 10 2 ͒, respectively. The solutions with moments in the basal plane are no longer tetragonal and therefore independent m x and m y components are allowed.…”

Section: Structure and Properties Of Ndcoaso (X =1)mentioning

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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“…High pressure studies on iron arsenide superconductors (for a review see paper of C.W. Chu and B. Lorenz [14]) reveal complex behavior, where dT c /dP may be positive and negative, depending on pressure and doping. These publications motivated us to study FeSe at pressures higher than 1.5 GPa.…”

Section: Introductionmentioning

confidence: 99%

Interplay between magnetism and superconductivity and the appearance of a second superconducting transition in α-FeSe at high pressure

Sidorov

Tsvyashchenko

Садыков

2009

J. Phys.: Condens. Matter

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We synthesized tetragonal a-FeSe by melting a powder mixture of iron and selenium at high pressure. Subsequent annealing at normal pressure results in removing traces of hexagonal bFeSe, formation of a rather sharp transition to superconducting state at T c ~ 7 K, and the appearance of a magnetic transition near T M = 120 K. Resistivity and ac-susceptibility were measured on the annealed sample at hydrostatic pressure up to 4.5 GPa. A magnetic transition visible in ac-susceptibility shifts down under pressure and the resistive anomaly typical for a spin density wave (SDW) antiferromagnetic transition develops near the susceptibility anomaly. T c determined by the appearance of a diamagnetic response in susceptibility, increases linearly under pressure at a rate dT c /dP = 3.5 K/GPa. Below 1.5 GPa, the resistive superconducting transition is sharp; the width of transition does not change with pressure; and, T c determined by a peak in dr/dT increases at a rate ~ 3.5 K/GPa. At higher pressure, a giant broadening of the resistive transition develops. This effect cannot be explained by possible pressure gradients in the sample and is inherent to a-FeSe. The dependences dr(T)/dT show a signature for a second peak above 3 GPa which is indicative of the appearance of another superconducting state in a-FeSe at high pressure. We argue that this second superconducting phase coexists with SDW antiferromagnetism in a partial volume fraction and originates from pairing of charge carriers from other sheets of the Fermi surface.2 Introduction Recent discovery of high T c superconductivity in layered iron arsenides [1][2][3][4] extended the family of unconventional superconductors. Previous work on high T c cuprates and heavy fermion superconductors prepared a basis for rapid progress in research on these new materials. The proximity to a magnetic instability, complex gap function, and coexistence of magnetism and superconductivity provide a key framework for future understanding the pairing mechanism of iron-based superconductors. The common structural feature of all these materials is layers composed of edge-sharing FeAs 4 -tetrahedra, separated by rare-earth-oxygen or alkaline-earth layers. The tetragonal a-phase of iron selenide has a structure composed of a stack of edge-sharing FeSe 4 -tetrahedra layer by layer, without any additional separating elements and may be regarded as an end member of a series of ironbased superconductors. Therefore, the discovery of superconductivity in a-FeSe with T c = 7 K [5] attracted considerable attention. Specific heat [5] and NMR [6] measurements indicate the unconventional nature of superconductivity in a-FeSe with lines of vanishing gap on the Fermi surface. In spite of the relatively simple structure of this binary compound, the preparation of a single phase sample is a challenge. Standard solid state reaction usually results in two or more phases in the sample, the impurity hexagonal b-phase being dominant [5][6][7][8][9]. In the first publications on superconductivity in iron seleni...

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High pressure studies on Fe-pnictide superconductors

Cited by 106 publications

References 74 publications

Non-linear lattice response of Sm oxypnictides to hydrostatic pressure

Non-linear lattice response of Sm oxypnictides to hydrostatic pressure

Superconductivity inNdFe1−xCoxAsO(

Interplay between magnetism and superconductivity and the appearance of a second superconducting transition in α-FeSe at high pressure

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