Mutliple-gap Superconductivity of Nonmagnetic Stoichiometric CaKFe4As4 Pnictide

Abstract

Using incoherent multiple Andreev reflection effect spectroscopy of planar break-junctions, we have studied the superconducting gap structure of CaKFe₄As₄ pnictides (the 1144 family), those turning to the superconducting state in the stoichiometric composition with critical temperature T_c ≈ 36.1K.We have shown a coexistence of three bulk superconducting order parameters Δ_i, and directly determined their magnitudes and corresponding characteristic ratios 2Δ_i(0)/k_BT_c ≈ 5.6, 3.9, and 1.3 at T \( \ll \) T_c. We compare the gap structure of CaKFe₄As₄ and sister pnictides of the 1144 and 122 families studied by us earlier.