Point-contact study of ReFeAsO1 - xFx (Re = La, Sm) superconducting films

Point-contact (PC) Andreev-reflection (AR) measurements of the superconducting gap in iron-oxypnictide ReFeAsO_{1 - x}F_x (Re = La, Sm) films have been carried out. The value of the gap is distributed in the range 2\Delta \simeq 5-10 meV (for Re = Sm) with a maximum in the distribution around 6 meV. The temperature dependence of the gap Δ(T) can be fitted well by a BCS curve giving a reduced gap ratio 2\Delta /kT_{

{c}}^*\simeq 3.5 (here T_c^* is the critical temperature from the BCS fit). At the same time, an expected second larger gap feature was difficult to resolve distinctly on the AR spectra, making the reliability of determination of the second gap questionable. Possible reasons for this, and the origin of other features like clear-cut asymmetry in the AR spectra and current regime in PCs, are discussed.