Failure of Mott's formula for the thermopower in carbon nanotubes

Well-known Mott's formula links the thermoelectric power characterized by the Seebeck coefficient to conductivity. We calculate analytically the thermoelectric current and Seebeck coefficient in one-dimensional systems and show that, while the prediction of Mott's formula is valid for Dirac fermions, it is misleading for the carriers having a parabolic dispersion. We apply the developed formalism to metallic single wall carbon nanotubes and obtain a nontrivial nonmonotonic dependence of the Seebeck coefficient on the chemical potential. We emphasize that, in contrast to Mott's formula, the classical Kelvin's formula that links thermoelectric power to the temperature derivative of the chemical potential is perfectly valid in carbon nanotubes in the ballistic regime. Interestingly, however, the Kelvin's formula fails in two- and three-dimensional systems in the ballistic regime.