Superconducting properties of the Fe-based layered superconductor LaFeAsO0.9F0.1-δ

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/kT(c)approximate to 3.5-4.2. Furthermore, we show that the new superconductor has electron-type conducting carriers with a rather low-carrier density.