Electronic correlations in the superconductor LaFeAs O0.89 F0.11 with low carrier density

The crystal structure and numerous normal and superconducting state properties of layered tetragonal (P4 nmm) LaFeAsO, with F doping of 11%, are reported. Resistivity measurements give an onset transition temperature Tc =28.2 K, and low field magnetic susceptibility data indicate bulk superconductivity. In applied magnetic field, analysis of the resistive transition results in a critical field Hc2 30 T and a coherence length ξGL 35. An upper limit for the electron carrier concentration of 1× 1021 cm-3 is inferred from the Hall data just above Tc. Strong electron-electron correlations are suggested from temperature-dependent resistivity, Seebeck coefficient, and thermal conductivity data. Anomalies near Tc are observed in both Seebeck coefficient and thermal conductivity data.