Pulsed versus d.c. I-V characteristics of charge-ordered LuFe$_{2}$O$_{4}$

We report on electronic transport measurements in a polycrystalline sample of LuFe$_{2}$O$_{4}$, over a wide range of electric fields and at temperatures above 230 K , - the range of temperatures was limited by the high resistivity of the sample . This work was motivated by reports about striking non-linear conductivity in polycrystals and single crystals of this multiferroic, in relatively moderate electric fields. Using short ($\sim $msec) single current pulses four probe measurements detected no deviations from linearity in the I-V characteristics, in fields up to E $\approx $ 500 V/cm. However, strong non-linearity and hysteresis were found in d.c. measurements at fields that decreased with increasing temperatures, suggesting self-heating. We include a set of oscillograms showing the time dependence of the voltages between the various probes at fixed current and temperature, which emphasize the importance of time domain studies of non-linear conductivity effects. We gratefully acknowledge Prof. Young Sun from the Institute of Physics, Chinese Academy of Sciences, Beijing, P.R. China, for providing us with the LuFe$_{2}$O$_{4}$ sample.