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

Journal Article · Mon Jul 30 04:00:00 EDT 2012 · Physical Review B

DOI:https://doi.org/10.1103/PhysRevB.86.020508· OSTI ID:1053252

Cho, Kyuil; Tanatar, Makariy A; Spyrison, Nicholas; Kim, Hyunsoo; Song, Y; Dai, Pengcheng; Zhang, C L; Prozorov, Ruslan

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.

• Research Organization: Ames Laboratory (AMES), Ames, IA (United States)
• Sponsoring Organization: USDOE Office of Science (SC)
• DOE Contract Number: AC02-07CH11358
• OSTI ID: 1053252
• Report Number(s): IS-J 7792; Journal Serial ID: 0198-0121/2012/86(2)/020508(5)
• Journal Information: Physical Review B, Journal Name: Physical Review B Journal Issue: 2 Vol. 86
• Country of Publication: United States
• Language: English

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36 MATERIALS SCIENCE