Suppression of tunnel transport by magnetic field in polypyrrole

Abstract

The anomalous charge transport in conducting polymer polypyrrole from the resistivity measurements at low temperature is due to the presence of polarons and bipolarons in these materials. The deviation from the hopping fit in the resistivity in the region below 4 K is attributed to the tunneling contribution to the conductivity. The number of bipolarons is larger in heavily doped samples leading to higher resistivity values at low temperatures, than in lightly doped samples, due to the low mobility of bipolarons. Tunnel transport becomes more difficult in the presence of a magnetic field due to the shrinkage of the Bohr radius of localised states.