Transport, optical, and electronic properties of the half-metal ${\mathrm{CrO}}_2$

The electronic structure of ${\mathrm{CrO}}_2$ is critically discussed in terms of the relation of existing experimental data and well converged local-spin-density approximation (LSDA) and generalized gradient approximation (GGA) calculations of the electronic structure and transport properties of this half metal magnet, with a particular emphasis on optical properties. We find only moderate manifestations of many-body effects. Renormalization of the density of states is not large and is in the typical range for transition metals. We find substantial deviations from Drude behavior in the far-infrared optical conductivity. These appear because of the unusually low energy of interband optical transitions. The calculated mass renormalization is found to be rather sensitive to the exchange-correlation functional used and varies from 10% (LSDA) to 90% (GGA), using the latest specific-heat data. We also find that dressing of the electrons by spin fluctuations, because of their high energy, renormalizes the interband optical transition at as high as 4 eV by about 20%. Although we find no clear indications of strong correlations of the Hubbard type, strong electron-magnon scattering related to the half metallic band structure is present and this leads to a nontrivial temperature dependence of the resistivity and some renormalization of the electron spectra.