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

作者：Cho K; Tanatar M A; Spyrison N; Kim H; Song Y; Dai Pengcheng; Zhang C L; Prozorov R^*

来源：Physical Review B, 2012, 86(2): 020508.

DOI：10.1103/PhysRevB.86.020508

The London penetration depth was measured in single crystals of self-doped Na1-delta FeAs (from under doping to optimal doping, T-c 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, Delta lambda(T) = AT(n), with the exponent that varies in a domelike fashion from n similar to 1.1 in the underdoped, reaching a maximum of n similar to 1.9 in the optimally doped, and decreasing again to n similar to 1.3 on the overdoped side. While the anisotropy of the gap structure follows a universal domelike evolution, the exponent at optimal doping, n similar to 1.9, is lower than in other charge-doped Fe-based superconductors (FeSCs). The full-temperature range superfluid density, rho(s)(T) = [lambda(0)/lambda(T)](2), at optimal doping is also distinctly different from other charge-doped FeSCs but is similar to isovalently substituted BaFe2(As1-x P-x)(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.

• 出版日期2012-7-30