Doping-dependent anisotropic superconducting gap in Na1−δ(Fe1−xCox)As from London penetration depth

K. Cho; M. A. Tanatar; N. Spyrison; H. Kim; Y. Song; Pengcheng Dai; C. L. Zhang; R. Prozorov

doi:10.1103/PhysRevB.86.020508

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Doping-dependent anisotropic superconducting gap in Na1−δ(Fe1−xCox)As from London penetration depth

K. Cho, M. A. Tanatar, N. Spyrison, H. Kim, Y. Song, Pengcheng Dai, C. L. Zhang, R. Prozorov

DOI 10.1103/PhysRevB.86.020508 · Physical Review B

T1

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Abstract

The London penetration depth was measured in single crystals of self-doped Na1−δFeAs (from under doping to optimal doping, Tc from 14 to 27 K) and electron-doped Na(Fe1−xCox)As with x ranging from undoped, x=0, to overdoped, x=0.1. In all samples, the low-temperature variation of the penetration depth exhibits a power-law dependence, Δλ(T)=ATn, with the exponent that varies in a domelike fashion from n∼1.1 in the underdoped, reaching a maximum of n∼1.9 in the optimally doped, and decreasing again to n∼1.3 on the overdoped side. While the anisotropy of the gap structure follows a universal domelike evolution, the exponent at optimal doping, n∼1.9, is lower than in other charge-doped Fe-based superconductors (FeSCs). The full-temperature range superfluid density, ρs(T)=λ(0)/λ(T)2, at optimal doping is also distinctly different from other charge-doped FeSCs but is similar to isovalently substituted BaFe2(As1−xPx)2, believed to be a nodal pnictide at optimal doping. These results suggest that the superconducting gap in Na(Fe1−xCox)As is highly anisotropic even at optimal doping.

Source-reported materials — not catalogue approval

Formula	Reported Tc (K)	Pressure (GPa)	Type
Na1-δFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	14	Pressure not reported	onset
Na1-δFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	27	Pressure not reported	onset
Na1-δFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	22	Pressure not reported	onset
NaFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	18	Pressure not reported	unknown
NaFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	31	3 GPa	unknown
LiFeAs Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	18	Pressure not reported	unknown
NaFe0.975Co0.025As Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	27	Pressure not reported	onset
NaFe0.95Co0.05As Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown
NaFe0.972Co0.028As Archive — visibility unverified Source-occurrence policy only; no material identity or catalogue acceptance is inferred from the formula.	—	Pressure not reported	unknown