Possible Multigap Superconductivity in SmFeAsO_(0.8)F_(0.2) A Point-contact Andreev-reflection Spectroscopy Study

摘要

We discuss the results of point-contact Andreev-reflection spectroscopy (PCAR) measurements in SmFeAsO_(0.8)F_(0.2) state-of-the-art polycrystals, with critical temperature T_c ≈ 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 MgB_2 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 positiveegative bias. The gaps obtained from the fit are Δ_1 = 6.15 ± 0.45 meV and Δ_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.