Multiple gaps revealed by low temperature specific heat in the 1111-type CaFe_0.88Co_0.12AsF single crystals

Low-temperature specific heat (SH) is measured on the 1111-type CaFe_0.88 Co_0.12AsF single crystals under different magnetic fields. A clear SH jump with the height mJ mol⁻¹ K⁻² is observed at the superconducting transition temperature T _c. The electronic SH coefficient increases linearly with the field below 5 T and a kink is observed around 5 T, indicating a multi-gap feature in the present system. Such a sign is also reflected in the T _c  −  B data. A detailed analysis shows that this behavior can be interpreted in terms of a two-gap scenario with the ratio –4.5. (paper)