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 to 3.1 eV for different temperatures from 30 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 quasiparticles with a mass renormalization factor of 5. 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.