Electronic correlations in the superconductorLaFeAsO0.89F0.11with low carrier density

The crystal structure and numerous normal and superconducting state properties of layered tetragonal $(P4∕nmm)$ LaFeAsO, with F doping of $\approx 11\%$, are reported. Resistivity measurements give an onset transition temperature $T_c=28.2\mathrm{K}$, and low field magnetic susceptibility data indicate bulk superconductivity. In applied magnetic field, analysis of the resistive transition results in a critical field $H_{c2}\approx 30\mathrm{T}$ and a coherence length ${\xi }_{\mathrm{GL}}\approx 35\mathrm{\AA }$. An upper limit for the electron carrier concentration of $1\times {10}^{21}{\mathrm{cm}}^{-3}$ is inferred from the Hall data just above $T_c$. Strong electron-electron correlations are suggested from temperature-dependent resistivity, Seebeck coefficient, and thermal conductivity data. Anomalies near $T_c$ are observed in both Seebeck coefficient and thermal conductivity data.