Full Gap Superconductivity in Ba_<0.6>K_<0.4>Fe_2As_2 Probed by Muon Spin Rotation(Condensed matter: electronic structure and electrical, magnetic, and optical properties)

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Superfluid density (n_s) in the mixed state of an iron pnictide superconductor Ba_<1-x>K_xFe_2As_2 is determined by muon spin rotation for a sample with optimal doping (x=0.4). The temperature dependence of n_s is perfectly reproduced using the conventional BCS model for s-wave paring, where the order parameter can be either a single-gap structure with Δ=8.35(6)meV [2Δ/k_BT_c=5.09(4)] or double-gap structure with Δ_1=12meV(fixed)[2Δ_1/k_BT_c=7.3] and Δ_2=6.8(3)meV [2Δ_2/k_BT_c=4.1(2)]. The latter is consistent with the recent result obtained by the angle-resolved photoemission spectroscopy. The large gap parameters (2Δ/k_BT_c) indicate the extremely strong coupling of carriers to bosons that mediate the Cooper pairing.
社団法人日本物理学会の論文
2009-02-15