The Electronic and Lattice Vibrational Properties of various ground states of Ge-doped FeGa3.

FeGa$_{3}$ has been investigated for its large thermopower effect at low temperatures, and the effects of electron correlations such as insulator to metal crossover, non-Fermi liquid behavior, and ferromagnetism. Furthermore, a ground state crossover from an insulator to paramagnetic and then to a ferromagnetic metal has been observed in Ge-doped FeGa$_{3}$. The large thermopower effect has been discussed to be a result of strong electron correlations or of the electron-phonon drag effect. In this study, we present the optical reflectance measurements for single crystals of FeGa$_{3-x}$Ge$_{x}$, for different values of x. The measurements were taken at varying temperatures from 300K to 5K, over a frequency range of 40 cm$^{-1}$ to 50000 cm$^{-1}$. We use Kramers-Kronig transformation to obtain various optical functions and compare the electronic and lattice vibrational properties of different ground states formed by Ge-substitution at Ga sites in FeGa$_{3}$. We also discuss that our observations show that the electron-phonon drag effect may have a greater contribution in the large thermopower effect.