▎ 摘　　要

The phonon-drag thermopower is studied in a monolayer graphene on a piezoelectric substrate. The phonon-drag contribution S-PA(g) from the extrinsic potential of piezoelectric surface acoustic (PA) phonons of a piezoelectric substrate (GaAs) is calculated as a function of temperature T and electron concentration n(s). At a very low temperature, S-PA(g) is found to be much greater than S-DA(g) of the intrinsic deformation potential of acoustic (DA) phonons of the graphene. There is a crossover of S-PA(g) and S-DA(g) at around similar to 5 K. In graphene samples of about > 10 mu m size, we predict S-g similar to 20 mu V at 10 K, which is much greater than the diffusion component of the thermopower and can be experimentally observed. In the Bloch-Gruneisen (BG) regime T and n(s) dependence are, respectively, given by the power laws S-PA(g) (S-DA(g)) similar to T-2(T-3) and S-PA(g), S-DA(g) similar to n(s)(-1/2) The T(n(s)) dependence is the manifestation of the 2D phonons (Dirac phase of the electrons). The effect of the screening is discussed. Analogous to Herring's law (S-g mu(p) similar to T-1), we predict a new relation S-g mu(p) similar to n(s)(0), where mu(p) is the phonon- limited mobility. We suggest that the ns dependent measurements will play a more significant role in identifying the Dirac phase and the effect of screening.