Low-temperature Hall effect and thermoelectric power in metallic PF6-doped polypyrrole

The Hall coefficient and the thermoelectric power of PF6-doped polypyrrole exhibiting metallic temperature dependence in the resistivity below 20 K are presented. It is remarkable that the Hall coefficient is negative and increases by cooling down to 0.5 K, in contrast to the acceptor doping and the decrease in the resistivity. The thermoelectric power becomes almost zero or weakly negative in the metallic region although it is positive and has almost linear temperature dependence above 50 K. It is also shown that the onset temperature of the metallic conductance is raised by the pressure.