中文题名: | 层间耦合对双层graphene能带结构的影响 |
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保密级别: | 公开 |
学科代码: | 070201 |
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学生类型: | 学士 |
学位: | 理学学士 |
学位年度: | 2012 |
学校: | 北京师范大学 |
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提交日期: | 2012-05-17 |
答辩日期: | 2012-05-24 |
外文题名: | Effect of Interlayer Coupling on the Band Structure of Twisted Bilayer Graphene |
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中文摘要: |
本文中,主要讲述通过紧束缚近似及其二次量子化,建立数学模型,来求解单层石墨烯(SLG)、双层石墨烯(BLG)、双层有夹角的石墨烯(TBG)的能带结构。在对SLG的模型构建中,我们考虑到了次近邻间的耦合强度,得出其能量色散关系解析式,其结果与已有的科研文献结果相符的很好。对于BLG,其能量色散关系为二次型,层间加置偏压后,其能带将会打开一个可调控的能隙。我们在计算TBG的模型后,得出其结果与AB堆垛方式的BLG不一样,倒和SLG有相同之处。我们得到:(a)费米面附近的能量呈线性色散关系;(b)层间外加偏压后,不会打开能隙;(c)层间耦合作用越强,低能区的两个范霍夫奇异点的距离越近;(d)小角度时,TBG的费米速度随层间夹角变大而变大,逐渐趋近SLG的费米速度。然而TBG的理论结果(d)与最新的实验结果不符合,因此我们对模型做出了相关修正。
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外文摘要: |
In this thesis, we studied the dispersion of the electronic bands in the single-layer graphene (SLG), bilayer graphene (BLG) and the twisted bilayer graphene (TBG) by the tight-binding approximation. For the calculation of SLG, we derive an analytic expression for the tight-binding dispersion including up to the second-nearest neighbors, and the results are consistent with what have been published in literature. For BLG, we find its dispersion of the electronic bands is quadratic. When applying a gate bias, we demonstrate that the electronic gap of BLG can be controlled externally. We consider a graphene bilayer with a relative small angle rotation between the layers. Contrary to what happens in an AA stacked bilayer and in accord with observations in monolayer graphene, we find: (a) the low energy dispersion is linear, as in a single layer; (b) an external electric field, perpendicular to the layers, does not open an electronic gap; (c) the more powerful the interlayer coupling is, the closer the distance is between two VHS; (d) the Fermi velocity of it can be significantly smaller than the single-layer value. However, based on the discrepancy between the model predictions in (d) and recent experiment results, thus the model is further revised in the article.
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参考文献总数: | 24 |
插图总数: | 29 |
插表总数: | 4 |
馆藏号: | 本070201/1208 |
开放日期: | 2012-05-31 |