Andreev spectroscopy of EuCsFe$_4$As$_4$ stoichiometric superconducting pnictide

EuCsFe$_4$As$_4$ pnictide (1144 family) single crystals with a critical temperature of $T_c \approx 36.8$ K and optimal superconducting properties in the stoichiometric composition are grown. Multiple-gap superconductivity determined by bulk order parameters $\Delta_L^{\rm out}$, $\Delta_L^{\rm in}$, and $\Delta_S$ with characteristic ratios $2\Delta_L^{\rm out}(0)/k_BT_c \approx 5.3$, $2\Delta_L^{\rm in}(0)/k_BT_c \approx 3.2$, and $2\Delta_S(0)/k_BT_c \approx 1.3$, respectively, is found for the first time below Tc using incoherent multiple Andreev reflection effect spectroscopy. It is shown that the gap structure of EuCsFe$_4$As$_4$ is similar to that of BaFe$_{2-x}$Ni$_x$As$_2$ superconducting pnictides of the sister 122 family.