▎ 摘　　要

The in-plane phonon-drag thermopower S (g), diffusion thermopower S (d) and the power factor PF are theoretically investigated in a twisted bilayer graphene (tBLG) as a function of twist angle theta, temperature T and electron density n (s) in the region of low T (1-20 K). As theta approaches magic angle theta (m), the S (g) and S (d) are found to be strongly enhanced, which is manifestation of great suppression of effective Fermi velocity v (F) * of electrons in moire flat band near theta (m). This enhancement decreases with increasing theta and T. In the Bloch-Gruneisen (BG) regime, it is found that S (g) similar to v (F) (*-2), T (3) and n (s) (-1/2). As T increases, the exponent delta in S (g) similar to T (delta) , changes from 3 to nearly zero and a maximum S (g) value of similar to 10 mV K-1 at similar to 20 K is estimated. S (g) is found to be larger (smaller) for smaller n (s) in low (high) temperature region. On the other hand, S (d), taken to be governed by Mott formula with S (d) similar to v (F) (*-1), T and n (s) (-1/2) and S (d) MUCH LESS-THAN S (g) for T > similar to 2 K. The power factor PF is also shown to be strongly theta dependent and is very much enhanced. Consequently, possibility of a giant figure of merit is discussed. In tBLG, theta acts as a strong tuning parameter of both S (g) and S (d) and PF in addition to T and n (s). Our results are qualitatively compared with the measured out-of-plane thermopower in tBLG.