Observation of negative differential mobility and charge packet in polyethylene

Charge packet has been observed on many occasions but its physical mechanisms have never been properly understood. One of the models proposed by Lewis et al shows the presence of negative differential mobility with an electric field in semicrystalline polyethylene. In this paper we have observed the negative differential mobility using the transient space charge profile measured by the pulsed electroacoustic technique. By superimposing a short pulse voltage to a dc voltage, it is possible to obtain the velocity of holes at different applied fields. To the best of our knowledge we have for the first time observed negative differential mobility in polyethylene. This observation provides crucial evidence to support Lewis's model and allows one to simulate charge packet and its behaviours.