Evidence for two-gap nodeless superconductivity in SmFeAsO$_{0.8}$F$_{0.2}$ from point-contact Andreev-reflection spectroscopy

TL;DR

This study provides evidence for two distinct nodeless superconducting gaps in SmFeAsO_{0.8}F_{0.2} using point-contact Andreev-reflection spectroscopy, revealing complex multigap superconductivity in this material.

Contribution

The paper demonstrates the presence of two nodeless superconducting gaps in SmFeAsO_{0.8}F_{0.2} through detailed spectroscopy analysis, advancing understanding of its superconducting properties.

Findings

Identification of two superconducting gaps at 6.15 meV and 18 meV.

Both gaps close at the same temperature following BCS behavior.

Single-band fit cannot fully explain the conductance curves.

Abstract

Point-contact Andreev-reflection measurements were performed in SmFeAsO_{0.8}F_{0.2} polycrystals with T_c \simeq 53 K. The experimental conductance curves reproducibly exhibit peaks around \pm 6 mV and shoulders at V \sim 16-20 mV, indicating the presence of two nodeless superconducting gaps. While the single-band Blonder-Tinkham-Klapwijk fit can only reproduce a small central portion of the conductance curve, the two-gap one accounts remarkably well for the shape of the whole experimental dI/dV. The fits of the normalized curves give Delta_1(0) = 6.15 \pm 0.45 meV and Delta_2(0) = 18 \pm 3 meV. Both gaps close at the same temperature and follow a BCS-like behavior.