Kubakaddi S S
Department of Physics, KLE Technological University, Hubballi-580031, Karnataka, India.
J Phys Condens Matter. 2021 May 13;33(24). doi: 10.1088/1361-648X/abf0c2.
The in-plane phonon-drag thermopower, diffusion thermopowerand the power factor PF are theoretically investigated in a twisted bilayer graphene (tBLG) as a function of twist angle, temperatureand electron densityin the region of low(1-20 K). Asapproaches magic angle, theandare found to be strongly enhanced, which is manifestation of great suppression of effective Fermi velocityof electrons in moiré flat band near. This enhancement decreases with increasingand. In the Bloch-Grüneisen (BG) regime, it is found that∼,and. Asincreases, the exponentin∼, changes from 3 to nearly zero and a maximumvalue of ∼10 mV Kat ∼20 K is estimated.is found to be larger (smaller) for smallerin low (high) temperature region. On the other hand,, taken to be governed by Mott formula with∼,andand≪for> ∼2 K. The power factor PF is also shown to be stronglydependent and is very much enhanced. Consequently, possibility of a giant figure of merit is discussed. In tBLG,acts as a strong tuning parameter of bothandand PF in addition toand. Our results are qualitatively compared with the measured out-of-plane thermopower in tBLG.
理论上研究了扭曲双层石墨烯（tBLG）中面内声子拖拽热功率、扩散热功率和功率因子PF随扭曲角、温度和电子密度在低温（1 - 20K）区域的变化。当接近魔角时，发现面内声子拖拽热功率和扩散热功率显著增强，这是在魔角附近莫尔平带中电子有效费米速度受到极大抑制的表现。这种增强随着温度和电子密度的增加而减小。在布洛赫 - 格律恩森（BG） regime中，发现面内声子拖拽热功率约为 ，扩散热功率约为 ，功率因子约为 。随着温度升高，面内声子拖拽热功率约为 中的指数 从 3 变为接近零，并且估计在约 20K 时最大值约为 10mV/K。发现在低温区域较小的温度下 较大（在高温区域较小）。另一方面，扩散热功率被认为由莫特公式控制，其中 约为 ， ，并且对于 > ∼2K， 远小于 。功率因子PF也显示出强烈依赖性并且显著增强。因此，讨论了获得巨大优值的可能性。在tBLG中，除了温度和电子密度之外，扭曲角还作为面内声子拖拽热功率、扩散热功率和PF的强调节参数。我们的结果与tBLG中测量的面外热功率进行了定性比较。
