Multiple-gap superconductivity of nonmagnetic stoichiometric CaKFe$_4$As$_4$ pnictide

Using incoherent multiple Andreev reflection effect spectroscopy of planar break-junctions, we have studied the superconducting gap structure of CaKFe$_4$As$_4$ pnictides (the $1144$ family), those turning to the superconducting state in the stoichiometric composition with critical temperature ${{T}_{{\text{c}}}} \approx 36.1$ K. We have shown a coexistence of three bulk superconducting order parameters ${{\Delta }_{i}}$, and directly determined their magnitudes and corresponding characteristic ratios $2{{\Delta }_{i}}(0){\text{/}}{{k}_{{\text{B}}}}{{T}_{{\text{c}}}} \approx 5.6, 3.9$, and $1.3$ at $T \ll {{T}_{{\text{c}}}}$. We compare the gap structure of CaKFe$_4$As$_4$ and sister pnictides of the $1144$ and $122$ families studied by us earlier.