Superconductivity in the iron-based F-doped layered quaternary compound Nd[O
                    <sub>1 − x</sub>
                    F
                    <sub>x</sub>
                    ]FeAs

[7,8] These discoveries have generated much interest in the mechanisms and manifestations of unconventional superconductivity in the family of doped quaternary layered oxypnictides LOMPn (L = La, Pr, Ce, Sm; M = Mn, Fe, Co, Ni; Pn=P, As) [9,10], because many features of these materials clearly set them apart from other superconductors. First, ab-initio calculations indicate that superconductivity originates from the d-orbitals of what would normally be expected to be pairbreaking magnetic Fe ions, suggesting that new non-phonon pairing mechanisms are responsible for the high T c [11,12]. Second, F-doped LaFeAsO is a semimetal, which exhibits strong ferromagnetic and antiferromagnetic fluctuations and a possible spin density wave instability around 150K in the parent undoped LaFeAsO [5,[13][14][15][16]. And third, superconductivity emerges on several disconnected pieces of the Fermi surface [11,12,17,18], thus exhibiting the multi-gap pairing, which has recently attracted so much attention in MgB 2 [19].Given the importance of magnetic correlations in the doped oxypnictides, transport measurements at very high magnetic fields are vital to probe the mechanisms of superconductivity. Indeed, first measurements of the upper critical field B c2 at low fields B < 7T have yielded a slope B c2 / (T c ) = dB c2 /dT º 2T/K near T c , for both La and Sm based oxypnictides [2][3][4][5][6]. From the conventional one-band Werthamer-Helfand-Hohenberg (WHH) theory [20] such slopes already imply rather high values B c2 (0) = 0.69T c B c2/ º 36T for LaFeAsO 0.89 F 0.1 , B c2 (0) º 59.3T for SmFeAsO 0.89 F 0.1 , and B c2 (0) º 72 T for PrFeAsO 0.89 F 0.1 , all well above B c2 of Nb 3 Sn. However, studies of the high-field superconductivity in MgB 2 alloys have shown that the upward curvature of B c2 (T) resulting from the multiband effects can significantly increase B c2 (0) as compared to the WHH one-band extrapolation (see, e.g., the review [21] and references therein). To address these important issues, we have performed high-field dc transport measurements on LaFeAsO 0.89 F 0.1 samples up to 45T. We show that B c2 (T) indeed exhibits two-gap behavior similar to that in MgB 2 , and B c2 (0) values exceed the WHH extrapolation by the factor ~ 2. Moreover, the observed B c2 (0) also exceeds the BCS paramagnetic limitPolycrystalline LaFeAsO 0.89 F 0.11 samples were made by solid state synthesis [4]. A sample ~ 3 x 1 x 0.5 mm was used for our four probe transport measurements in the 45T Hybrid magnet at the NHMFL, supplemented by low field measurements in a 9T superconducting magnet. Our low-field data agreed well with the earlier data taken at ORNL on the same sample [4], indicating its good temporal and atmospheric stability. The 45T Hybrid magnet was swept only from 11.5T to 45T due to the constant 11.5T background of the outsert magnet while lower fields were swept from 0T to 9T in a PPMS with resistivity measured in AC mode using a 5mA excitation current, whereas the high field resistance R(B) was measured by a Keithley nanovo...

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confidence: 99%

Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields

Hunte

Jaroszyński

Gurevich

et al. 2008

Nature

572

566

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“…The RE(O 1−x F x )FeAs (1111 phase) for the different rare earths (La, Ce, Pr, Gd, Sm and Nd) show varying superconducting transition temperature (T c ) as replacing lanthanum with heavier rare-earth elements resulted in an increase of T c from 26K to above 55K [1,[6][7][8][9][10][11]. Interestingly, these compounds are similar to the High T c cuprate superconductors (HTSc cuprates) in terms of their layered structure, low carrier density and magnetically ordered parent phase [12].…”

Section: Introductionmentioning

confidence: 99%

Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Agx doping (x = 0.0–0.3)

Rani

Hafiz

Awana

2016

Physica C: Superconductivity and its Applications

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“…[1][2][3][4] In the ZrCuSiAs-type REFeP nO compounds (RE = rare earth, P n = pnictogen), the 4f -electrons usually form an antiferromagnetic (AFM) order at very low temperatures, while the occurrence of superconductivity is mainly associated with the Fe-3d electrons. [5][6][7][8][9] For instance, CeFeAsO sequentially undergoes two AFM-type transitions upon cooling from room temperature, one associated with Fe (T Fe N ≈ 150 K) and the other one attributed to Ce (T Ce N ≈ 3.4 K). 9,10 Elemental substitutions in CeFeAsO, e.g., Fe/Co or As/P, may induce superconductivity while suppressing the magnetic order of Fe-3d electrons.…”

Section: Introductionmentioning

confidence: 99%

Magnetocrystalline anisotropic effect inGdCo1−xFexAsO(x=0,0.05)

et al. 2015

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Superconductivity in the iron-based F-doped layered quaternary compound Nd[O _{1 − x} F _x ]FeAs

Cited by 782 publications

References 8 publications

Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields

Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields

Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Agx doping (x = 0.0–0.3)

Magnetocrystalline anisotropic effect inGdCo1−xFexAsO(x=0,0.05)

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Superconductivity in the iron-based F-doped layered quaternary compound Nd[O 1 − x F x ]FeAs

Cited by 782 publications

References 8 publications

Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields

Two-band superconductivity in LaFeAsO0.89F0.11 at very high magnetic fields

Improvement in granularity of NdFeAsO0.8F0.2 superconductor through Agx doping (x = 0.0–0.3)

Magnetocrystalline anisotropic effect inGdCo1−xFexAsO(x=0,0.05)

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Superconductivity in the iron-based F-doped layered quaternary compound Nd[O _{1 − x} F _x ]FeAs