Superconducting Properties of the Fe-Based Layered SuperconductorLaFeAsO0.9F0.1−δ

Abstract

We have employed a new route to synthesize single phase F-doped LaOFeAs compound and confirmed the superconductivity above 20 K in this Fe-based system. We show that the new superconductor has a rather high upper critical field of over 50 T. A clear signature of superconducting gap opening below $T_c$ was observed in the far-infrared reflectance spectra, with $2\Delta /{\mathrm{kT}}_c\approx 3.5–4.2$. Furthermore, we show that the new superconductor has electron-type conducting carriers with a rather low-carrier density.