Multiple gaps revealed by low temperature specific heat in the 1111-type CaFe0.88Co0.12AsF single crystals

Low-temperature specifc heat (SH) is measured on the 1111-type CaFe0.88 Co0.12AsF single crystals under different magnetic felds. A clear SH jump with the height ∆C/T|Tc = 10.4 mJ mol-1 K-2 is observed at the superconducting transition temperature Tc. The electronic SH coeffcient ∆γ(B) increases linearly with the feld 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 Tc - B data. A detailed analysis shows that this behavior can be interpreted in terms of a twogap scenario with the ratio ∆L/∆S = 2.8–4.5.