  It is known that electron scattering by surface polar phonons (SPPs) of the
substrate reduces their mobility in supported graphene. However, there is no
experimental evidence for contribution of drag of electrons by SPP to
thermoelectric phenomena in graphene: graphene thermopower exhibits good
agreement with Mott's law, which means that the diffusion contribution to the
thermopower is dominant in a wide range of carrier densities and temperatures.
Here we develop a complete theory of drag of electrons in graphene by SPP. By
solving Boltzmann transport equation for electrons scattered by SPPs we derive
SPP drag contribution to the thermopower in graphene. Compared to diffusion
thermopower, obtained values appear to be one order of magnitude lower for
various substrates. This can be explained by low occupation number of the SPPs
and short mean free path of such phonons stemming from their small group
velocity. We conclude that experiments on thermopower in graphene can be
treated within the framework of Mott's law.
