  On the basis of self-consistent Born approximation for Dirac fermions under
charged impurity scatterings in graphene, the theory for calculating the
thermo-electric power is developed by using the heat current-current
correlation function. The advantage of the present approach is its ability to
effectively treat the low doping case where the coherence process involving
carriers in both upper and lower bands becomes important. We show that the low
temperature behavior of the thermo-electric power as function of the carrier
concentration and the temperature observed by the experiments can be
successfully explained by our calculation.
