Full Gap Superconductivity in Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ Probed by Muon Spin Rotation

Abstract

Superfluid density ($n_s$) in the mixed state of an iron pnictide superconductor Ba${}_{0.6}$K${}_{0.4}$Fe${}_2$As${}_2$ is determined by muon spin rotation for a sample with optimal doping ($x=0.4$). The temperature dependence of $n_s$ is perfectly reproduced by the conventional BCS model for s-wave paring, where the order parameter can be either a single-gap with $\Delta =8.35(6)$ meV [$2\Delta /k_B{T}_c=5.09(4)$], or double-gap structure with ${\Delta }_1=12$ meV (fixed) [$2{\Delta }_1/k_B{T}_c=7.3$] and ${\Delta }_2=6.8(3)$ meV [$2{\Delta }_2/k_B{T}_c=4.1(2)$]. The latter is consistent with the recent result of angle-resolved photo-emssion spectroscopy. The large gap parameters ($2\Delta /k_B{T}_c$) indicate extremely strong coupling of carriers to bosons that mediate the Cooper pairing.

arXiv comment4 pages, 3 figures

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