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Mukuda, H.; Furukawa, Satoshi; Kinouchi, Hiroaki; Yashima, M.; Kitaoka, Y.; Shirage, Parasharam M.; Eisaki, H.; Iyo, A.

doi:10.1103/physrevlett.109.157001

Cited by 13 publications

(14 citation statements)

References 37 publications

(48 reference statements)

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“…by means of 31 P-NMR for the present samples, which are compared with 75 As-NMR results for Y0.95La0.05FeAsO δ (Tc=50 K) 27 , Y0.2La0.8FeAsO δ (Tc=34 K) 29 , and LaFeAsO δ (Tc=28 K) 30 .…”

Section: Discussionmentioning

confidence: 99%

“…On the other hand, for the LaFeAs(O 1−y F y ) series, the maximum T c emerges at y=0.1 without any development of AFMSFs upon cooling down to T c 14,15,23 , although AFMSFs can be observed in the vicinity of the AFM ordered phase with a lower T c , i.e., in the range of 0.04 < y < 0.08 [24][25][26] . In this context, we emphasize 27,29,30 . According to the spin-fluctuation mediated SC mechanism, the large Fermi surface multiplicity in Ln1111 in addition to the presence of AFMSFs is an another crucial factor for enhancing T c , which is optimized when the FeAs 4 tetrahedron is close to a regular one realized in Ln1111 28 .…”

Section: Discussionmentioning

confidence: 99%

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Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(
Mukuda
¹
,
Engetsu
²
,
Yamamoto
³

et al. 2014
Phys. Rev. B
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Systematic31 P-NMR studies on LaFe(As1−xPx)(O1−yFy) with y=0.05 and 0.1 have revealed that the antiferromagnetic spin fluctuations (AFMSFs) at low energies are markedly enhanced around x=0.6 and 0.4, respectively, and as a result, Tc exhibits respective peaks at 24 and 27 K against the P substitution for As. This result demonstrates that the AFMSFs are responsible for the increase in Tc for LaFe(As1−xPx)(O1−yFy) as a primary mediator of the Cooper pairing. From a systematic comparison of AFMSFs with a series of (La1−zYz)FeAsO δ compounds in which Tc reaches 50 K for z=0.95, we remark that a moderate development of AFMSFs causes Tc to increase up to 50 K under the condition that the local lattice parameters of the FeAs tetrahedron approach those of the regular tetrahedron. We propose that Tc of Fe-pnictides exceeding 50 K is maximized under an intimate collaboration of the AFMSFs and other factors originating from the optimization of the local structure.

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Section: Discussionmentioning

confidence: 99%

Section: Discussionmentioning

confidence: 99%

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(
Mukuda
¹
,
Engetsu
²
,
Yamamoto
³

et al. 2014
Phys. Rev. B
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0
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“…However, note that AFMSFs at low energies are not always highly significant in Fe pnictide compounds with T c > 50 K. 29 Recently, another type of stripe AFM(H) phase carrying a large AFM moment but exhibiting a low T N has been reported for heavily electron-doped compounds LaFeAs(O,H):…”

Section: 23mentioning

confidence: 99%

Emergence of Novel Antiferromagnetic Order Intervening between Two Superconducting Phases in LaFe(As₁₋_xP_x)O: ³¹P-NMR Studies

et al. 2014

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Systematic31 P-NMR studies of LaFe(As1−xPx)O compounds have revealed the emergence of a novel antiferromagnetic ordered phase (AFM-2) at 0.4≤ x ≤0.7 that intervenes between two superconductivity (SC) phases. This AFM-2 phase with Néel temperature TN= 35 K for x=0.6 is in strong contrast to the AFM order (AFM-1) at x=0 exhibiting TN of 140 K. Previous 31 P-NMR studies of LaFe(As1−xPx)(O1−yFy) have revealed that Tc reaches a maximum of 24 K for x=0.6 as a result of the marked enhancement of AFM spin fluctuations at low energies due to electron doping by the flourine substitution of y=0.05 for oxygen. The reason for this unexpected result has been found in the present work, that is, the emergence of AFM-2 at 0.4 ≤ x ≤0.7 without electron doping. We note that AFM spin fluctuations arising from interband nesting on the dXZ/dY Z orbits must be a key factor for the occurrence of SC around AFM-2.Iron (Fe) oxypnictide LaFeAsO with an orthorhombic structure exhibits antiferromagnetic (AFM) order, and the substitution of F − for O 2− induces superconductivity (SC) with a maximum transition temperature of T c =26 K in LaFeAsO 1−y F y .1 The isostructural compound LaFeP(O 1−y F y ) with P substituted for As also reveals the SC transition at T c =4 -7 K, which is lower than that in the case of LaFeAs(O,F).2 In Fepnictide superconductors, T c reaches a maximum of 55 K 3, 4 when a FeAs 4 block forms a nearly regular tetrahedral structure:5 The optimal values of the As-Fe-As bonding angle (α), the height of pnictogen (h Pn ) from the Fe plane, and the a-axis length (a) are 109.5• , 5∼1.38Å, 6 and ∼3.9Å, 4 respectively. In this context, since the substitution of P for As makes the a-axis length smaller, α wider, and h Pn smaller than the optimal values for high-T c Fe pnictides, it is anticipated that T c might decrease monotonically as x increases in solid solution compounds LaFe(As 1−x P x )(O 1−y F y ). Unexpectedly, T c exhibits a nonmonotonic variation with x in LaFe(As 1−x P x )(O 1−y F y ) compounds.7-9 Previous 31 P-NMR studies of these compounds have revealed that T c reaches its respective maxima of 27 and 24 K for x=0.4 with y=0.1 and for x=0.6 with y=0.05, as a result of the marked enhancement of AFM spin fluctuations(AFMSFs) at low energies.10 The result provides clear evidence that T c is enhanced by AFMSFs at low energies even though the lattice parameters deviate from their optimum values. However, another question should be addressed: Why are AFMSFs enhanced despite the fact that the lattice parameters of the compounds are far from those of the AFM mother compound LaFeAsO.In this Letter, we report the results of our 31 P-NMR studies that a novel AFM ordered phase (AFM-2) emerges at 0.4 ≤ x ≤0.7, intervening between two SC phases (SC-1 and SC-2) in LaFe(As 1−x P x )O. The 31 P- * E-mail: mukuda@mp.es.osaka-u.ac.jp † NMR Knight shift indicates the appearance of a sharp density of states (DOS) at the Fermi level derived from a d 3Z 2 −r 2 orbit, which is less relevant with the onset of SC-2. On the other hand, AFMSF...

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“…4(b), some samples such asR1111OF, electron-doped perovskiteblock-type compound Ca 4 (Mg 0.25 Ti 0.75 ) 3 O 7.5 Fe 2 As 2 (T c ∼ 45 K), 46 electron-doped 112-type compound Ca 0.88 La 0.12 Fe(As 0.9 Sb 0.1 ) 2 (T c ∼47K), 47 and the hole doped 122 compound BaK122(T c =38K) 48 are always characterized by h P n = 1.35 ∼ 1.4 Å and the bond angle of P n-Fe-P n α ∼ 109.5 • , in which the local lattice parameters of the FeAs layer are close to the values for regular FeAs 4 tetrahedron 2,3 . Note that in such compounds the T dependence of 1/T 1 T tends to saturate towards T c and/or show the broad maximum above T c , as reported in (Y 0.95 La 0.05 )1111(T c =50 K), 24,59 Ca 4 (Mg,Ti) 3 Fe 2 As 2 O 8−y (T c = 45 K), 60 Sr 4 (Mg 0.3 Ti 0.7 ) 2 O 6 Fe 2 As 2 (T c =34 K) 61 , and so on. As for the 122 series, although the low energy AFM-SFs are significantly observed in BaK122 34,[56][57][58] , the relationship between the T c and QCP in the phase diagram was not clearly revealed in Ba 1−x K x Fe 2 As 2 56 .…”

Section: Discussionmentioning

confidence: 59%

NMR evidence for an intimate relationship between antiferromagnetic spin fluctuations and extended s-wave superconductivity in mono-crystalline SrFe2(As_{1-x}P_{x})2

Miyamoto,

Mukuda,

Kobayashi

et al. 2015

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We report systematic 31 P-NMR study on iron (Fe)-based superconductors SrFe2(As1−xPx)2 (Sr122AsP), in which a superconducting (SC) transition temperature Tc at x=0.35 increases from Tc=26 K up to 33 K by annealing an as-grown mono-crystalline sample. The present NMR study has unraveled that Tc reaches a highest value of 33 K at x=0.35 around a quantum critical point at which antiferromagnetic (AFM) order disappears. When noting that the SC transition disappears at x=0.6 where the AFM spin fluctuations (SFs) are no longer present, we remark that the onset and increase of Tc are apparently associated with the emergence and enhancement of AFM-SFs, respectively. In the SC state, the residual density of state (RDOS) at the Fermi energy EF in the SC state becomes much smaller for the annealed sample than for the as-grown one, suggesting that some inhomogeneity and/or imperfection for the latter increases RDOS as expected for unconventional SC state with nodal gap. These findings in Sr122AsP are consistent with the unconventional s±-wave Cooper pairing state that is mediated by AFM-SFs. We also discuss other key-ingredients besides the AFM-SFs to increase Tc further.

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High-TcNodelesss±-wave Superconductivity in(Y,

Cited by 13 publications

References 37 publications

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(
Mukuda
¹
,
Engetsu
²
,
Yamamoto
³

et al. 2014
Phys. Rev. B
Self Cite
28
10
33
0
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Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(
Mukuda
¹
,
Engetsu
²
,
Yamamoto
³

et al. 2014
Phys. Rev. B
Self Cite
28
10
33
0
View full text Add to dashboard Cite

Emergence of Novel Antiferromagnetic Order Intervening between Two Superconducting Phases in LaFe(As₁₋_xP_x)O: ³¹P-NMR Studies

NMR evidence for an intimate relationship between antiferromagnetic spin fluctuations and extended s-wave superconductivity in mono-crystalline SrFe2(As_{1-x}P_{x})2

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High-TcNodelesss±-wave Superconductivity in(Y,

Cited by 13 publications

References 37 publications

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(Mukuda1, Engetsu2, Yamamoto3 et al. 2014Phys. Rev. BSelf Cite2810330View full textAdd to dashboardCite

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(Mukuda1, Engetsu2, Yamamoto3 et al. 2014Phys. Rev. BSelf Cite2810330View full textAdd to dashboardCite

Emergence of Novel Antiferromagnetic Order Intervening between Two Superconducting Phases in LaFe(As1−xPx)O: 31P-NMR Studies

NMR evidence for an intimate relationship between antiferromagnetic spin fluctuations and extended s-wave superconductivity in mono-crystalline SrFe2(As_{1-x}P_{x})2

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About

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(
Mukuda
¹
,
Engetsu
²
,
Yamamoto
³

et al. 2014
Phys. Rev. B
Self Cite
28
10
33
0
View full text Add to dashboard Cite

Enhancement of superconducting transition temperature due to antiferromagnetic spin fluctuations in iron pnictides LaFe(As1−xPx)(
Mukuda
¹
,
Engetsu
²
,
Yamamoto
³

et al. 2014
Phys. Rev. B
Self Cite
28
10
33
0
View full text Add to dashboard Cite

Emergence of Novel Antiferromagnetic Order Intervening between Two Superconducting Phases in LaFe(As₁₋_xP_x)O: ³¹P-NMR Studies