Phonon-drag thermopower in an armchair graphene nanoribbon.

We calculate the phonon-drag thermopower S(g) of an armchair graphene nanoribbon (AGNR) in the boundary scattering regime of phonons. S(g) is studied as a function of temperature, Fermi energy and width of the AGNR. At very low temperatures T, S(g) is exponentially suppressed and an activated behavior is observed which is characteristic of one-dimensional carriers. This is in contrast to the power law dependence in graphene in the Bloch-Grüneisen regime. However, at higher T, S(g) in the AGNR levels off. S(g) also shows strong dependence on Fermi energy and width of the AGNR. The magnitude of S(g) in the AGNR is compared with that in single-wall carbon nanotube and graphene.