Magnetic penetration depth of single crystal SmFeAsO_{1-x}F_y: a fully gapped superconducting state

Abstract

We report measurements of the in-plane magnetic penetration depth $\lambda$ in single crystals of SmFeAsO${}_{1-x}$F${}_y$ ($x\simeq y\simeq 0.2$) with $T_c\simeq 45$ K. We find that at low temperature $\lambda$ has an exponential temperature dependence which suggests that the Fermi surface is fully gapped. The magnitude of the minimum energy gap, ${\Delta }_1=1.1\pm 0.1k_B{T}_c$ at T=0 K, is significantly smaller than the BCS weak-coupling value suggesting that the gap is either strongly anisotropic or varies significantly between the different Fermi surface sheets. Our data fits well a two gap model with an additional larger gap of magnitude ${\Delta }_2=1.8\pm 0.2k_B{T}_c$ which is associated with $\sim 80$% of the total superfluid density.

arXiv comment4 pages with figures

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