Very high thermoelectric power factor near magic angle in twisted bilayer graphene
Very high thermoelectric power factor near magic angle in twisted bilayer graphene
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DOI：
10.1088/2053-1583/ac161d
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发表时间：
2021-03
期刊：
影响因子：
5.5
通讯作者：
A. Kommini;Z. Akšamija
中科院分区：
文献类型：
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作者：
A. Kommini;Z. Akšamija
最近对扭曲双层石墨烯（TBG）的研究发现，其扭曲角相关的电子结构导致了许多独特的性质，如超导性，相关绝缘态和磁性。在TBG中以低扭曲角出现的平坦带导致电子态密度的尖锐特征，影响输运。在这里，我们表明，他们导致上级和可调热电（TE）的性能。结合一个迭代玻尔兹曼输运方程求解器和电子结构从一个精确的连续模型，我们计算TE输运性质的TBG在不同的扭曲角，载流子密度，和温度。我们的模拟显示，TBG的室温TE功率因数（PF）达到40 mW m−1 K−2，显著高于单层石墨烯，是迄今为止报道的最高值。峰PF在魔角附近观察到，在扭转角为1.3 °，并且接近完全带填充。我们阐明，它的依赖性是由两个相反的力量驱动：之间的带隙的平坦和远程带抑制双极输运，提高塞贝克系数，但差距与扭转角减小;另一方面，费米速度，影响电导率，是最小的魔角和扭转角的上升。我们观察到随着温度的降低，TBG的PF进一步增加。强大的TE性能，沿着的能力，微调运输使用扭曲角，使TBG的一个有趣的候选人，为未来的研究和应用在能量转换和热传感和管理。
Recent research on twisted bilayer graphene (TBG) uncovered that its twist-angle-dependent electronic structure leads to a host of unique properties, such as superconductivity, correlated insulating states, and magnetism. The flat bands that emerge at low twist angles in TBG result in sharp features in the electronic density of states, affecting transport. Here we show that they lead to superior and tuneable thermoelectric (TE) performance. Combining an iterative Boltzmann transport equation solver and electronic structure from an exact continuum model, we calculate TE transport properties of TBG at different twist angles, carrier densities, and temperatures. Our simulations show the room-temperature TE power factor (PF) in TBG reaches 40 mW m−1 K−2, significantly higher than single-layer graphene and among the highest reported to date. The peak PF is observed near the magic angle, at a twist angle of ≈1.3∘, and near complete band filling. We elucidate that its dependence is driven by two opposing forces: the band gap between the flat and remote bands suppresses bipolar transport and improves the Seebeck coefficient but the gap decreases with twist angle; on the other hand, the Fermi velocity, which impacts conductivity, is smallest at the magic angle and rises with twist angle. We observed a further increase in the PF of TBG with decreasing temperature. The strong TE performance, along with the ability to fine-tune transport using twist angle, makes TBG an interesting candidate for future research and applications in energy conversion and thermal sensing and management.