Evidence for two-gap nodeless superconductivity in SmFeAsO1−xFx from point-contact Andreev-reflection spectroscopy

Abstract

Point-contact Andreev-reflection spectroscopy measurements were performed in SmFeAsO1−xFx polycrystals with x=0.09 (Tc≃42 K) and x=0.20 (Tc≃52 K). In all cases the experimental conductance curves reproducibly exhibit low-energy peaks and higher-energy shoulders (at 4–6 and 16–20 meV, respectively, for x=0.20), which indicate the presence of two nodeless superconducting gaps. While the single-band Blonder-Tinkham-Klapwijk model can only reproduce a small central portion of a given conductance curve, the two-gap one accounts remarkably well for the shape of the whole experimental dI/dV vs V curve. The fit of the normalized curves gives Δ1(0)=6.15±0.45 meV and Δ2(0)=18±3 meV for x=0.20, while for x=0.09 the values Δ1(0)=4.9±0.5 meV and Δ2(0)=15±1 meV are obtained. In all cases, both gaps close at the same temperature and follow a BCS-like behavior.

Source-reported materials — not catalogue approval

Similar papers