Optical properties of LuFe$_2$O$_4$

We measured the optical properties of single crystalline LuFe$_2$O$_4$ as a function of temperature and compared the results with recent electronic structure calculations. The 300 K optical gap is found to be ${\sim}$ 0.4 eV. The optical conductivity is very sensitive to temperature and shows a sharp transition at around 170 K structural transition. The Fe$^{2+}$ to Fe$^{3+}$ charge transfer transition (at approximately 1.5 eV) sharpens dramatically at low temperature, a trend that may be connected with the complex charge order of the material. Preliminary high energy magneto-dielectric data will be discussed.