  We present magneto-transport measurements performed on underdoped PCCO at THz
frequencies as a function of temperature and doping. A rapidly decreasing Hall
mass is observed as the doping is reduced consistent with the formation of
small electron Fermi pockets. However, both dc and infrared (IR)
magneto-transport data strongly deviate from the predictions of transport
theory in the relaxation time approximation (RTA) based on angular resolved
photoemission data. The Hall mass is observed to increase continuously with
increasing temperature with no signature at the Neel temperature. In the
paramagnetic state, the temperature dependence of the Hall mass is consistent
with current vertex corrections to the Hall conductivity due to magnetic
fluctuations as observed in overdoped PCCO. Possible causal mechanisms for the
discrepancy between transport theory within the RTA and the magneto-transport
data are discussed.
