The Effect of Ge-doping on Electronic and Lattice Vibrational Properties of FeGa₃

Studied initially for its large thermopower effect, the intermetallic semiconductor FeGa₃ has recently been shown to provide a suitable platform for studying electron correlations, such as metal-insulator transition, non Fermi liquid behavior and ferromagnetism. In particular, with Ge-doping at Ga site the ground state is tuned from a Kondo insulator to a paramagnetic and further to a ferromagnetic metal. Here we present optical reflectance measurements on single crystals of FeGa_3-xGe_x, for different values of x. The temperature was varied between 300 K and 5 K, and the frequency ranged from 40 cm^-1 to 50 000 cm^-1. Involving the Kramers-Kronig transformation, we obtained various optical functions and discuss the electronic and lattice vibrational properties of different ground states resulting from Ge substitution.