Possible Three-Dimensional Nodes in thes± Superconducting Gap of BaFe₂(As_1-xP_x)₂

Abstract

We theoretically examine the superconducting state of BaFe 2 (As 1Àx P x ) 2 , an isovalent doping 122-iron-pnictide superconductor. We construct a three-dimensional 10-orbital model by first-principles band calculation, and investigate the superconducting gap within the spin-fluctuation-mediated pairing mechanism. The gap is basically sAE, where the gap changes its sign between electron and hole Fermi surfaces, but three-dimensional nodal structures appear in the largely warped hole Fermi surface having a strong Z 2 =XZ=YZ orbital character. The present result, together with our previous study of the 1111 systems, explains the strong material dependence of the superconducting gap in iron pnictides.

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

“…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 nodal to nodeless state as h Pn is tuned, for example, in underdoped BaFe 2 ðAs 1Àx P x Þ 2 .…”

“…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].…”

“…For underdoped Ba 1Àx K x Fe 2 As 2 , it is still not clear how the superconducting gap transforms from nodeless to nodal at x % 0:16 [14]. The remaining three compounds, BaFe 2 ðAs 1Àx P x Þ 2 , LaFePO, and LiFeP, have stimulated various interpretations of the effect of isovalent P doping [21][22][23][24][25].…”

“…For LaFePO, Kuroki et al have attributed the low-T c nodal pairing to the lack of Fermi surface around (, ) in the unfolded Brillouin zone, due to the low pnictogen height [21]. For BaFe 2 ðAs 1Àx P x Þ 2 , Suzuki et al have proposed a three-dimensional nodal structure in the largely warped hole Fermi surface and no nodes on the electron Fermi surface [24]. This proposal is supported by recent ARPES experiments that found a nodal gap in the expanded -hole pocket at k z ¼ in BaFe 2 ðAs 0:7 P 0:3 Þ 2 [44].…”

Effects of c/a Anisotropy and Local Crystal Structure on Superconductivity in AFe2(As1−xPx)2 (A = Ba1−ySry, Sr1−yCay and Eu)

“…5, 6) Furthermore, the study of angle-resolved photoemission spectroscopy (ARPES) 7) demonstrated that the observed FSs fulfill the nesting condition between the electron and hole FSs, which was consistent with the spin fluctuation theory in Ba122P. 8,9) From the crystallographic viewpoint, the appearance of SC would be ascribed to the optimization of the pnictogen (Pn) height from the Fe layer (h Pn ) 10) or the Pn-Fe-Pn bond angle (α), 11) which was also explained by nesting-based theories. 9,12) On the other hand, according to the nesting scenario, the distance between neighboring Fe layers, which must be correlated with interlayer hybridization and thus with anisotropy, should have a distinct influence on antiferromagnetism (AFM) and SC.…”