Discrete conductance switching in conducting polymer wires

Charge transport in conducting polymers ~polyaniline and polypyrrole! bridged between two gold nanoelectrodes separated with a nanoscale gap ~varying from ;1 nm to a few tens of nm was studied by controlling the polymer redox states electrochemically. In sharp contrast to the macroscopic samples, the conductance switches abruptly between insulating ~off! and conducting ~on! states like a telegraphic signal. The time durations of the on and off states depend on the potential of the nanoelectrodes, indicating the important role of the redox states in the signal. We attribute the telegraphic signal to the fluctuation between the insulating reduced state and conducting oxidized state of the polymer, which rises as electrons trap into the oxidized state and escape from the reduced state.