TY  - JOUR
T1  - Anisotropic London penetration depth and superfluid density in single crystals of iron-based pnictide superconductors
JO  - Physica C: Superconductivity
VL  - 469
IS  - 9-12
SP  - 582
EP  - 589
PY  - 
T2  - Superconductivity in Iron-Pnictides
AU  - Prozorov, R.
AU  - Tanatar, M.A.
AU  - Gordon, R.T.
AU  - Martin, C.
AU  - Kim, H.
AU  - Kogan, V.G.
AU  - Ni, N.
AU  - Tillman, M.E.
AU  - Bud'ko, S.L.
AU  - Canfield, P.C.
SN  - 0921-4534
M3  - doi: DOI: 10.1016/j.physc.2009.03.012
UR  - http://www.sciencedirect.com/science/article/B6TVJ-4VW554V-5/2/3c6e88e73f9da76360cfbf7796cd4ba0
KW  - Penetration depth
KW  - Anisotropy
KW  - Pairing symmetry
KW  - Pnictide
AB  - 
In- and out-of-plane magnetic penetration depths were measured in three iron-based pnictide superconducting systems. The "122" system was represented by electron-doped Ba(Fe1-xCox)2As2 with the doping through the whole phase diagram with x [approximate] 0.038, 0.047, 0.058, 0.074 and 0.10 (Tc ranged from 13 to 24 K) and by hole-doped (Ba1-xKx)Fe2As2 with doping close to optimal, with measured x [approximate] 0.45 (Tc [approximate] 28 K) and an underdoped sample with x [approximate] 0.15 (Tc [approximate] 19 K). The "1111" system was represented by single crystals of NdFeAs(O1-xFx) with nominal x = 0.1 (Tc [approximate] 43 K). All studied samples of both 122 systems show a robust power-law behavior, [lambda](T)[is proportional to]Tn, with the sample-dependent exponent n = 2-2.5, which is indicative of unconventional pairing. This scenario could be possible either through scattering in a S± state or due to nodes in the superconducting gap. In the Nd-1111 system, the interpretation of the results is complicated by magnetism of the rare-earth ions. For all three systems, the anisotropy ratio, [gamma][lambda][reverse not equivalent][lambda]c/[lambda]ab, was found to decrease with increasing temperature, whereas the anisotropy of the coherence lengths, , has been found to increase (both opposite to the trend in two-band MgB2). The overall anisotropy of the pnictide superconductors is small, in fact much smaller than that of the cuprates (except YBa2Cu3O7-x (YBCO)). The 1111 system is about two times more anisotropic than the 122 system. Our data and analysis suggest that the iron-based pnictides are complex superconductors in which a multiband three-dimensional electronic structure and strong magnetic fluctuations play important roles.
ER  -