In- and out-of-plane London penetration depths in single crystals of FeSe$_{0.4}$Te$_{0.6}$ superconductor

In- and out-of-plane London penetration depths $\lambda(T)$ were measured in single crystals of FeSe$_{0.4}$Te$_{0.6}$ superconductor by means of the tunnel diode resonator technique. The penetration depth does not show BCS-like exponential saturation at low temperature. Instead, we found that both $\Delta\lambda_{ab}(T)$ and $\Delta\lambda_{c}(T)$ has nearly quadratic behavior, similar to that observed in the FeAs-based superconductors. We also calculated the in-plane superfluid density $\rho^s(T)=\lambda^2(0)/\lambda^2(T)$, and fitted with various possible models.