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Xiao-Shu, Luo; Tanatar, M. A.; Reid, J.-Ph.; Shakeripour, H.; Doiron-Leyraud, N.; Ni, N.; Bud’ko, Sergey L.; Canfield, Paul C.; Luo, Huiqian; Wang, Zhaosheng; Wen, Hao; Prozorov, Ruslan; Taillefer, Louis

doi:10.1103/physrevb.80.140503

Cited by 118 publications

(107 citation statements)

References 37 publications

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“…The isovalently doped system BaFe 2 (As 1−x P x ) 2 of the 122 family is particularly interesting as signs of nodal behavior have been detected even at optimal doping [11][12][13][14][15] . This is in stark contrast with its hole-and electron-doped counterparts which, despite showing similar phase diagrams and critical temperatures, are believed to be nodeless at least at optimal doping [18][19][20][21] . Specific heat measurements have been performed on the hole-doped Ba 1−x K x Fe 2 As 2 18,22,23 and on the electron-doped Ba(Fe 1−x Co x ) 2 As 2 24-26 .…”

Section: Introductioncontrasting

confidence: 39%

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

et al. 2015

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We report on specific heat measurements on clean overdoped BaFe2(As1−xPx)2 single crystals performed with a high resolution membrane-based nanocalorimeter. A nonzero residual electronic specific heat coefficient at zero temperature γr = C/T |T →0 is seen for all doping compositions, indicating a considerable fraction of the Fermi surface ungapped or having very deep minima. The remaining superconducting electronic specific heat is analyzed through a two-band s-wave α model in order to investigate the gap structure. Close to optimal doping we detect a single zero-temperature gap of ∆0 ∼ 5.3 meV, corresponding to ∆0/kBTc ∼ 2.2. Increasing the phosphorus concentration x, the main gap reduces till a value of ∆0 ∼ 1.9 meV for x = 0.55 and a second weaker gap becomes evident. From the magnetic field effect on γr, all samples however show similar behavior [γr(H) − γr(H = 0) ∝ H n , with n between 0.6 and 0.7]. This indicates that, despite a considerable redistribution of the gap weights, the total degree of gap anisotropy does not change drastically with doping.

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Section: Introductioncontrasting

confidence: 39%

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

et al. 2015

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“…Those experiments have been further supported by measurements of bulk properties such as thermal conductivity [7][8][9]. On the overdoped (with respect to the optimal doping) side, nodal superconductivity has been found in the extremely hole-doped KFe 2 As 2 [10,11], while a strongly anisotropic nodeless gap [9] or isotropic nodeless gaps with significantly different magnitudes [12,13] have been suggested in heavily electron-doped BaðFe 1Àx Co x Þ 2 As 2 .…”

mentioning

confidence: 64%

Robust Nodal Superconductivity Induced by Isovalent Doping inBa(Fe1−xRux)2As2and
Qiu
¹
,
Zhou
²
,
Zhang
³

et al. 2012
Phys. Rev. X
43
1
17
0
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We present the ultra-low-temperature heat-transport study of iron-based superconductors BaðFe 1Àx Ru x Þ 2 As 2 and BaFe 2 ðAs 1Àx P x Þ 2 . For optimally doped BaðFe 0:64 Ru 0:36 Þ 2 As 2 , a large residual 0 =T at zero field and a ffiffiffiffi ffi H p dependence of 0 ðHÞ=T are observed, which provide strong evidences for nodes in the superconducting gap. This result demonstrates one more nodal superconductor in iron pnictides. The similarities between isovalent Fe and P dopings strongly suggest that the nodal superconductivity in Since the discovery of high-T c superconductivity in iron pnictides [1,2], the issue of what mechanisms underlie the electron pairing in these systems has been a central one [3]. One key step in resolving it is to clarify the symmetry and structure of the superconducting gap [4]. However, even for the most studied ðBa; Sr; Ca; EuÞFe 2 As 2 (122) system, the situation is still fairly complex [4].Near optimal doping where the T c is the highest, for both hole-and electron-doped 122 compounds, the angleresolved photon-emission-spectroscopy (ARPES) experiments have clearly demonstrated multiple nodeless superconducting gaps [5,6]. Those experiments have been further supported by measurements of bulk properties such as thermal conductivity [7][8][9]. On the overdoped (with respect to the optimal doping) side, nodal superconductivity has been found in the extremely hole-doped KFe 2 As 2 [10,11], while a strongly anisotropic nodeless gap [9] or isotropic nodeless gaps with significantly different magnitudes [12,13] have been suggested in heavily electron-doped BaðFe 1Àx Co x Þ 2 As 2 . On the underdoped side, recent heat-transport measurements have claimed possible nodes in the superconducting gap of hole-doped Ba 1Àx K x Fe 2 As 2 with x < 0:16 [14], in contrast to the nodeless gaps that have been found in electron-doped BaðFe 1Àx Co x Þ 2 As 2 [9]. It is hard to get a simple pairing mechanism from such complex situation of the superconducting gap structure.More intriguingly, nodal superconductivity has also been found in optimally doped BaFe 2 ðAs 0:67 P 0:33 Þ 2 (T c ¼ 30K) [15,16], in which the superconductivity is induced by isovalent P doping. Moreover, LaFePO (T c $6K) was found to display clear nodal behavior [17][18][19], and recently evidence for nodes in the superconducting gap of LiFeP (T c $ 4:5 K) has emerged from measurements of magnetic penetration depth [20]. The nodal superconductivity in these P-doped compounds is very striking, which raises the puzzling questions of whether, and why, the P doping is unique among iron-based superconductors. Although various theoretical explanations have been offered for this puzzle, investigators are far from reaching consensus [21][22][23][24][25].A recent empirical proposal is that the nodal state in ironpnictide superconductors, except for KFe 2 As 2 , is induced when the pnictogen height h Pn from the iron plane decreases below a threshold value of approximately 1:33 A [20]. According to this proposal, there may exist a transition from...

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“…(i) Near optimal doping, x ∼ 0.4, ARPES 25,26 , neutron scattering 27 , penetration depth 28 and thermal conductivity 29,30 measurements give strong evidence for nodeless, near-constant s± gap, which changes sign between hole and electron pockets. This is consistent with theoretical calculations [5][6][7][8]11,31 .…”

Section: Introductionmentioning

confidence: 99%

s+isstate with broken time-reversal symmetry in Fe-based superconductors

2013

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We analyze the evolution of the superconducting gap structure in strongly hole doped Ba1−xKxFe2As2 between x = 1 and x ∼ 0.4 (optimal doping). In the latter case, the pairing state is most likely s±, with different gap signs on hole and electron pockets, but with the same signs of the gap on the two Γ-centered hole pockets (a ++ state on hole pockets). In a pure KFe2As2 (x = 1), which has only hole pockets, laser ARPES data suggested another s± state, in which the gap changes sign between hole pockets (a +− state). We analyze how ++ gap transforms into a +− gap as x → 1. We found that this transformation occurs via an intermediate s + is, state in which the gaps on the two hole pockets differ in phase by φ, which gradually involves from φ = π (the +− state) to φ = 0 (the ++ state). This state breaks time-reversal symmetry and has huge potential for applications. We compute the dispersion of collective excitations and show that two different Leggett-type phase modes soften at the two end points of TRSB state.

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Quasiparticle heat transport in single-crystallineBa1−xKxFe2As2

Cited by 118 publications

References 37 publications

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

Robust Nodal Superconductivity Induced by Isovalent Doping inBa(Fe1−xRux)2As2and
Qiu
¹
,
Zhou
²
,
Zhang
³

et al. 2012
Phys. Rev. X
43
1
17
0
View full text Add to dashboard Cite

s+isstate with broken time-reversal symmetry in Fe-based superconductors

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Quasiparticle heat transport in single-crystallineBa1−xKxFe2As2

Cited by 118 publications

References 37 publications

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

Superconducting gap evolution in overdopedBaFe2(As1−xPx)2single crystals through nanocal

Robust Nodal Superconductivity Induced by Isovalent Doping inBa(Fe1−xRux)2As2andQiu1, Zhou2, Zhang3 et al. 2012Phys. Rev. X431170View full textAdd to dashboardCite

s+isstate with broken time-reversal symmetry in Fe-based superconductors

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Robust Nodal Superconductivity Induced by Isovalent Doping inBa(Fe1−xRux)2As2and
Qiu
¹
,
Zhou
²
,
Zhang
³

et al. 2012
Phys. Rev. X
43
1
17
0
View full text Add to dashboard Cite