Infrared and transport properties of LuFe2O4under electric fields

Multiferroic LuFe${}_{2}$O${}_{4}$ (LFO) exhibits three-dimensional (3D) charge order below ${T}_{\text{CO}}\ensuremath{\sim}$ 350 K and strong electroresistance (ER) above a static threshold field ${E}_{\mathrm{th}}$. By measuring simultaneously, in LFO single crystals, the dc current and the far-infrared reflectivity along different axes, we do not detect any insulator-to-metal transition above ${E}_{\mathrm{th}}$. Combined current-temperature measurements confirm that the ER is due to self-heating of LFO, as recently reported. The data can be fit by the standard activation law for an intrinsic semiconductor, with a gap value $\ensuremath{\Delta}$ = 0.57 eV. This value is consistent with that of the optical gap reported for LFO in the literature.