Optical evidence for heavy charge carriers in FeGe

The optical spectrum of the cubic helimagnetic metal FeGe has been investigated in the frequency range from 0.01 - 3.1 eV for different temperatures from 30 K to 296 K. The optical conductivity shows the evolution of a low energy (0.22 eV) interband transition and the development of a narrow free carrier response with a strong energy and temperature dependence. The frequency dependent effective mass and scattering rate derived from the optical data indicate the formation of dressed quasi-particles with a mass renormalization factor of 12. Similar to FeSi the spectral weight in FeGe is not recovered over a broad frequency range, an effect usually attributed to the influence of the on-site Coulomb interaction.