Possible Multigap Superconductivity in SmFeAsO0.8F0.2: A Point-contact Andreev-reflection Spectroscopy Study

We discuss the results of point-contact Andreev-reflection spectroscopy (PCAR) measurements in SmFeAsO0.8F0.2 state-of-the-art polycrystals, with critical temperature T (c)a parts per thousand 53 K. The low-temperature conductance curves show clear peaks at about 7 meV and additional shoulders at 16-20 meV. Their shape is similar to that of PCAR spectra in MgB2 and suggests the presence of two superconducting energy gaps even in this Fe-based superconductor. The fit of the conductance curves with a two-band BTK model, up to T (c), further supports this indication in spite of a marked asymmetry in the conductance curves for positive/negative bias. The gaps obtained from the fit are Delta(1)=6.15 +/- 0.45 meV and Delta(2)=18 +/- 3 meV, and they follow a nice BCS-like temperature dependence, closing both at the same T (c). Our results are discussed in comparison with experimental and theoretical results in this and other Fe-based superconductors.