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The paper reports complementary studies of the order parameter of the newly discovered iron-based superconductor, KCa2Fe4As4F2 (Tc = 34 K), that consists of alternating blocks of KFe2As2 (122) phase and CaFeAsF (1111) phase. We performed high-resolution intrinsic multiple Andreev reflection spectroscopy supplemented with self-field critical current measurements. Andreev spectra obtained by means of a break-junction technique reveal two distinct superconducting order parameters ΔL and ΔS. Their temperature dependencies were measured from 1.5 K to Tc. The shapes of Andreev reflections dips, corresponding to the two gaps are symmetrical, which is a signature of s-wave order parameter. Temperature dependence of the self-field critical current can also be described by two s-wave gaps model. [ABSTRACT FROM AUTHOR]

We compare the structure of the superconducting order parameter of overdoped BaFe1.88Ni0.12As2 and underdoped BaFe1.92Ni0.08As2 pnictides with similar K. Using incoherent multiple Andreev reflection effect spectroscopy, we directly determined the magnitudes of the two microscopic superconducting order parameters: the small superconducting gap and probably anisotropic large gap, their characteristic ratios and temperature dependences. We discuss similarity and difference in the gap structure, as well as possible influence of antiferromagnetic phase to superconducting properties. [ABSTRACT FROM AUTHOR]

EuCsFe4As4 pnictide (1144 family) single crystals with a critical temperature of Tc ≈ 36.8 K and optimal superconducting properties in the stoichiometric composition are grown. Multiple-gap superconductivity determined by bulk order parameters , , and with characteristic ratios , , and , respectively, is found for the first time below Tc using incoherent multiple Andreev reflection effect spectroscopy. It is shown that the gap structure of EuCsFe4As4 is similar to that of BaFe2 – xNixAs2 superconducting pnictides of the sister 122 family. [ABSTRACT FROM AUTHOR]

The structure of the superconducting order parameter of weakly underdoped BaFe1.92Ni0.08As2 pnictides with the critical temperature Tc ≈ 18.2 K has been determined. Two microscopic superconducting order parameters—the small superconducting gap ΔS(0) and, supposedly, the edges of the large gap with anisotropy in the ab plane and —have been determined at T ≪ Tc, together with their temperature dependences, using incoherent multiple Andreev reflection spectroscopy. It has been shown that the determined temperature dependence of the lower critical field Hc1(T) can be described in the two-band approximation both within the so-called alpha model (using experimental ΔS(0), , and values) and using the temperature dependences ΔS(T) and obtained by multiple Andreev reflection spectroscopy under the assumption of a fairly strong anisotropy of the small superconducting gap, where the experimental ΔS(0) value is taken as the outer edge of its angular distribution. [ABSTRACT FROM AUTHOR]

The current-voltage characteristics and dynamic conductance spectra of the SnS junction in Ba(Fe, Ni)2As2 superconducting pnictide of almost optimal composition have been obtained. A slight slope of the electronic density of states near the Fermi level has been detected. Using multiple Andreev reflection spectroscopy, we have directly determined the values and the temperature dependences of the two superconducting order parameters and estimated their anisotropy. We have shown that the obtained temperature dependences of Andreev excess current and Andreev zero-bias conductance could be fitted with a two-band model, and estimated the partial conductances of the two effective bands where the large and the small gaps are developed. [ABSTRACT FROM AUTHOR]

We compare the structure of the superconducting order parameter of overdoped BaFe1.88Ni0.12As2 and underdoped BaFe1.92Ni0.08As2 pnictides with similar K. Using incoherent multiple Andreev reflection effect spectroscopy, we directly determined the magnitudes of the two microscopic superconducting order parameters: the small superconducting gap and probably anisotropic large gap, their characteristic ratios and temperature dependences. We discuss similarity and difference in the gap structure, as well as possible influence of antiferromagnetic phase to superconducting properties. [ABSTRACT FROM AUTHOR]

The paper reports complementary studies of the order parameter of the newly discovered iron-based superconductor, KCa2Fe4As4F2 (Tc = 34 K), that consists of alternating blocks of KFe2As2 (122) phase and CaFeAsF (1111) phase. We performed high-resolution intrinsic multiple Andreev reflection spectroscopy supplemented with self-field critical current measurements. Andreev spectra obtained by means of a break-junction technique reveal two distinct superconducting order parameters ΔL and ΔS. Their temperature dependencies were measured from 1.5 K to Tc. The shapes of Andreev reflections dips, corresponding to the two gaps are symmetrical, which is a signature of s-wave order parameter. Temperature dependence of the self-field critical current can also be described by two s-wave gaps model. [ABSTRACT FROM AUTHOR]