J ul 2 01 9 Two-Gap Superconductivity in CaFe 0 . 88 Co 0 . 12 AsF Revealed by Temperature Dependence of the Lower Critical Field H cc 1 ( T )

anism of unconventional superconductors. Here we report an in-depth investigation on the out-of-plane lower critical fieldH c1 of fluorine-based 1111 system superconductor CaFe0.88Co0.12AsF with Tc = 21 K. A pronounced two-gap feature is revealed by the kink in the temperature dependent H c1(T ) curve. The magnitudes of the two gaps are determined to be ∆1 = 0.86 meV and ∆2 = 4.48 meV, which account for 74% and 26% of the total superfluid density respectively. Our results suggest that the local antiferromagnetic exchange pairing picture is