Superconductivity at 54 K in F-Free NdFeAsO<sub>1-<i>y</i></sub>

Kitô, Hijiri; Eisaki, H.; Iyo, A.

doi:10.1143/jpsj.77.063707

Cited by 314 publications

(296 citation statements)

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“…Hole doping, by substituting Sr 2+ for La 3+ results in T c = 25 K [32]. A series of oxygen deficient RFeAsO 1-δ have also been prepared by high pressure syntheses with highest T c = 55 K for SmFeAsO 0.85 [33][34][35]. Here we report of the synthesis and characterization of Co-doped LaFeAsO, and find superconductivity for ~ 4 -12% doping levels.…”

Section: Introductionmentioning

confidence: 96%

Superconductivity inLaFe1−xCoxAsO

et al. 2008

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Here we report the synthesis and basic characterization of LaFe 1-x Co x AsO for several values of x. The parent phase LaFeAsO orders antiferromagnetically (T N  145 K). Replacing Fe with Co is expected to both electron dope the system and introduce disorder in the FeAs layer. For x = 0.05 antiferromagnetic order is destroyed and superconductivity is observed at T c onset = 11.2 K. For x = 0.11 superconductivity is observed at T c onset = 14.3 K, and for x = 0.15 T c onset = 6.0 K. Superconductivity is not observed for x = 0.2 and 0.5, but for x = 1, the material appears to be ferromagnetic (T c  56 K) as judged by magnetization measurements. We conclude that Co is an effective dopant to induce superconductivity. Somewhat surprisingly, the system appears to tolerate considerable disorder in the FeAs planes.

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Section: Introductionmentioning

confidence: 96%

Superconductivity inLaFe1−xCoxAsO

et al. 2008

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“…Since the discovery of superconductivity in LaFeAs(O 1−x F x ) [1], high transition temperatures (T c ) up to 56 K have been reported in the doped Fe-based oxypnictides [2,3,4,5,6,7,8,9]. The new high-temperature superconductivity in Fe-pnictides has attracted tremendous interests both experimentally and theoretically.…”

Section: Introductionmentioning

confidence: 99%

Penetration depth, lower critical fields, and quasiparticle conductivity in Fe-arsenide superconductors

Shibauchi

Hashimoto

Okazaki

et al. 2009

Physica C: Superconductivity

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In this article, we review our recent studies of microwave penetration depth, lower critical fields, and quasiparticle conductivity in the superconducting state of Fe-arsenide superconductors. Highsensitivity microwave surface impedance measurements of the in-plane penetration depth λ ab in single crystals of electron-doped PrFeAsO1−y (y ∼ 0.1) and hole-doped Ba1−xKxFe2As2 (x ≈ 0.55) are presented. In clean crystals of Ba1−xKxFe2As2, as well as in PrFeAsO1−y crystals, the penetration depth shows flat temperature dependence at low temperatures, indicating that the superconducting gap opens all over the Fermi surface. The temperature dependence of superfluid density λ 2 ab (0)/λ 2 ab (T ) in both systems is most consistent with the existence of two different gaps. In Ba1−xKxFe2As2, we find that the superfluid density is sensitive to degrees of disorder inherent in the crystals, implying unconventional impurity effect. We also determine the lower critical field Hc1 in PrFeAsO1−y by using an array of micro-Hall probes. The temperature dependence of Hc1 saturates at low temperatures, fully consistent with the superfluid density determined by microwave measurements. The anisotropy of Hc1 has a weak temperature dependence with smaller values than the anisotropy of upper critical fields at low temperatures, which further supports the multi-gap superconductivity in Fe-arsenide systems. The quasiparticle conductivity shows an enhancement in the superconducting state, which suggests the reduction of quasiparticle scattering rate due to the gap formation below Tc. From these results, we discuss the structure of the superconducting gap in these Fe-arsenides, in comparison with the high-Tc cuprate superconductors.

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“…2,3,4 In addition, recently, high temperature superconductivity with similar properties has been found in simpler compounds based on FeAs sheets such as ThCr 2 Si 2 structure type (Ba,K)Fe 2 As 2 . 5,6 These Fe-based materials are commonly viewed as unconventional (non-electron-phonon) superconductors based on the high values of T c , the proximity to magnetism and the fact that calculations of the electron phonon coupling show that it is far too weak to account for the superconductivity.…”

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confidence: 96%