ИСТИНА

In order to directly determine the structure of the SC order parameter, we used incoherent multiple Andreev reflection effect (IMARE) spectroscopy. Andreev nanojunctions of the SC–thin normal metal–SC (SnS) type were formed at T = 4.2 K by a planar “break-junction” technique. Generally, IMARE causes an excess current at I(V) curve of SnS junction at any bias voltage eV, zero-bias conductance peak, and a series of SC gap features in the dI(V)/dV-spectrum. The positions of the latter directly relate with the SC gap magnitude at any temperature until Tc. The directly measured the temperature dependences of the SC gaps are typical for a moderate interband interaction. The anisotropy degree of the large SC gap AL remains almost constant with temperature until Tc. The SC gap structure of EuCsFe4As4 (the shape of dI(V)/dV spectra of SnS junctions, the values of AL and the characteristic ratios) and its temperature behaviour (Δ_i(T), A_L(T)) resemble those for Ba(Fe,Ni)2As2 pnictides studied by us earlier. Above Tc we reproducibly observed a residual nonlinearity of the d(V)/dV spectra of tunneling junctions, showing a normal-state dI(V)/dV hump at zero bias and dips at eV >> 2Δ_L. Such normal-state features could originate from the electron density of states (DOS) features in the vicinity if the Fermi level, or its renormalization by a resonant electron-phonon interaction.