Unconventional superconductivity in CaFe$_{0.85}$Co$_{0.15}$AsF evidenced by torque measurements

Out-of-plane angular dependent torque measurements were performed on CaFe$_{0.85}$Co$_{0.15}$AsF single crystals. Abnormal superconducting fluctuation, featured by enhanced diamagnetism with magnetic field, is detected up to about 1.5 times superconducting transition temperature $T_c$. Compared to cuprate superconductors, the fluctuation effect in iron-based superconductor is less pronounced. Anisotropy parameter $\gamma$ is obtained from the mixed state torque data and it is found that $\gamma$ shows both magnetic field and temperature depenence, pointing to multiband superconductivity. The temperature dependence of penetration depth $\lambda(T)$ suggests unconventional superconductivity in CaFe$_{0.85}$Co$_{0.15}$AsF.