Infrared and transport properties of LuFe(2)O(4) under electric fields

Multiferroic LuFe2O4 (LFO) exhibits three-dimensional (3D) charge order below TCO ~ 350 K and strong electroresistance (ER) above a static threshold field Eth. 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 Eth. 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 = 0.57 eV. This value is consistent with that of the optical gap reported for LFO in the literature.