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Enhancement of phonon-drag thermopower in bilayer graphene

机译：双层石墨烯中声子拖曳热能的增强

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Phonon-drag thermopower S~g is theoretically studied in a bilayer graphene (BLG). Two-dimensional (2D) electrons with chiral property, finite effective mass, and parabolic dispersion are assumed to interact with the 2D acoustic phonons having a linear dispersion via deformation-potential coupling. A comparison is made with the very recent experimental results of Nam et al. [arXiv: 1005.4739 (unpublished)] for 30≤T≤70 K. Numerically S~g is studied as a function of temperature T, electron concentration n_s, and phonon mean-free path. T3 behavior of S~g at very low T changes gradually to sublinear at higher T and the effect of chiral property of the electrons is seen explicitly. We suggest the possibility of significant enhancement of S~g at lower carrier concentrations by increasing the linear dimension of the sample and reducing its edge roughness. We find that S8 in BLG is enhanced by a factor of 7 compared with the magnitude of S~g in monolayer graphene, for n_s =0.5 × 10~(12) cm~(-2) in the Bloch-Griineisen (BG) regime. In BG regime S~g ～ T~3, a manifestation of 2D phonons with linear dispersion and 5~g ～ n~(-3/2), a characteristic of 2D electrons with parabolic dispersion. A comparison is also made with the results in conventional and ideal 2D systems. S~g is found to be very significant in comparison with the diffusion thermopower S~d and the latter is shown to be ～T, n_s~(-1) at low T and high n_s. Herring's law, S~gμp～T~(-1), relating phonon-limited mobility μ_p to S~g, is found to be valid in BLG.
机译：理论上在双层石墨烯（BLG）中研究了声子拖动热功率S〜g。假定具有手性，有限有效质量和抛物线色散的二维（2D）电子通过形变-电位耦合与具有线性色散的2D声子相互作用。与Nam等人最近的实验结果进行了比较。 [arXiv：1005.4739（未出版）]对于30≤T≤70K。在数值上研究了S〜g与温度T，电子浓度n_s和声子无均值路径的关系。 S〜g在非常低的T下的T3行为逐渐转变为在较高T下的亚线性，并且可以清楚地看到电子的手性性质的影响。我们建议通过增加样品的线性尺寸并降低其边缘粗糙度，可以在较低的载流子浓度下显着提高S〜g。我们发现，在Bloch-Griineisen（BG）机制中，n_s = 0.5×10〜（12）cm〜（-2）时，BLG中的S8与单层石墨烯中S〜g的大小相比提高了7倍。 。在BG态S〜g〜T〜3中，具有线性色散的二维声子的表现，而5〜g〜n〜（-3/2）是具有抛物线色散的二维电子的特征。还对常规和理想2D系统中的结果进行了比较。与扩散热功率S〜d相比，S〜g非常重要，后者在低T和高n_s时显示为〜T，n_s〜（-1）。在BLG中发现将声子极限迁移率μ_p与S〜g相关的鲱鱼定律S〜gμp〜T〜（-1）是有效的。

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