Abstract
The magnetic, transport, and optical properties of single crystals have been investigated parallel and perpendicular to the plane. The anisotropy depends only slightly on temperature. In both orientations, the spin-density-wave transition at shows up as a considerable increase in the dc resistivity. Susceptibility measurements evidence the magnetic order of the moments at with little influence on the electronic transport taking place in the FeAs layers. Polarization-dependent infrared spectroscopy reveals strongly anisotropic optical properties and yields a carrier density of only and a bandmass of . A sizeable Drude contribution is present at all temperatures and narrows upon cooling. Below , the spin-density-wave gap develops in the in-plane optical conductivity; no appreciable change is detected for the perpendicular polarization. Modifications in the phonon features are associated with changes in the electronic properties at . The extended Drude analysis yields a linear behavior of the frequency-dependent scattering rate below , indicating an interaction between the charge carriers and spin fluctuations in the spin-density-wave state.
1 More- Received 3 March 2009
DOI:https://doi.org/10.1103/PhysRevB.79.155103
©2009 American Physical Society