Sliding charge density waves in manganites?

We report on the linear and nonlinear conductivity measurements on charge-ordered La 1− x Ca x MnO 3 ( x≈0.5 and x=0.75). Upon cooling below room temperature, the onset of charge ordering— T co is marked by a peak in the logarithmic derivative of the resistivity ( d ln ρ/ d(1/ T)) and by a change in the slope of the thermopower as a function of temperature. The I– V characteristics of samples with negative coefficient of resistivity ( x=0.52 and 0.75) was measured by DC and pulsed currents. We show how the nonlinearity of the I– V characteristics vanishes when short, single current pulses are used. This work shows that when searching for dramatic phenomena such as sliding charge density waves in samples with negative temperature coefficient of resistivity, the first step should be to check if the I– V nonlinearity persists when using single, short current pulses.