Electron-phonon scattering and in-plane electric conductivity in twisted bilayer graphene
Electron-phonon scattering and in-plane electric conductivity in twisted bilayer graphene
复制标题
扭曲双层石墨烯中的电子声子散射和面内电导率
DOI：
10.1103/physrevb.94.245403
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发表时间：
2016
影响因子：
3.7
通讯作者：
S. Shallcross
中科院分区：
文献类型：
--
作者：
N. Ray. D. Weckbecker;S. Sharma;O. Pankratov;S. Shallcross
我们用(I)电子结构的低能有效哈密顿量，(Ii)各向同性弹性声子模型和(Iii)弹性电子-声子散射的线性Boltzmann方程研究了石墨烯扭转双层膜的面内输运性质。我们发现扭转双层中的输运对组成层的旋转角非常敏感。与扭转双层膜的电子结构类似，在三个不同的角度区域，输运性质是不同的。在大角度()和低于层间Bloch-Grüneisen温度K的温度下，电导率与扭角无关，即各层完全解耦。在这个温度以上，即使在基态解耦，这些层也被电子-声子散射重新耦合，并且输运既不同于单层石墨烯，也不同于伯纳尔双层膜。在小角区域，电导率下降了两个数量级，并表现出丰富的能量依赖性，反映了费米面潜在拓扑变化(Lifshitz转变)的复杂性。在中间角，电导率随着扭角的减小而不断减小，而电导率的能量依赖关系呈现出两个尖锐的跃迁，发生在特定的角度相关能量处，这可能与(I)扭曲双层膜的范霍夫奇点研究得很好和(Ii)当三角放置的电子口袋装饰强翘曲的狄拉克锥体时发生的Lifshitz跃迁有关。有趣的是，我们发现，在小角度范围内，电声散射主要由层对称弯曲声子主导，而在大角度范围内，层对称弯曲模才是最重要的。我们研究了一层垂直电场的作用，发现它在低温下对电导率有很大的影响，而这种影响在室温下被费米涂抹冲刷掉了。
We have surveyed the in-plane transport properties of the graphene twist bilayer using (i) a low-energy effective Hamiltonian for the underlying electronic structure, (ii) an isotropic elastic phonon model, and (iii) the linear Boltzmann equation for elastic electron-phonon scattering. We find that transport in the twist bilayer is profoundly sensitive to the rotation angle of the constituent layers. Similar to the electronic structure of the twist bilayer, the transport is qualitatively different in three distinct angle regimes. At large angles () and at temperatures below an interlayer Bloch-Grüneisen temperature ofK, the conductivity is independent of the twist angle, i.e., the layers are fully decoupled. Above this temperature the layers, even though decoupled in the ground state, are recoupled by electron-phonon scattering and the transport is different both from single-layer graphene as well as the Bernal bilayer. In the small-angle regime, the conductivity drops by two orders of magnitude and develops a rich energy dependence, reflecting the complexity of the underlying topological changes (Lifshitz transitions) of the Fermi surface. At intermediate angles, the conductivity decreases continuously as the twist angle is reduced, while the energy dependence of the conductivity presents two sharp transitions, that occur at specific angle-dependent energies, and that may be related to (i) the well-studied van Hove singularity of the twist bilayer and (ii) a Lifshitz transition that occurs when trigonally placed electron pockets decorate the strongly warped Dirac cone. Interestingly, we find that, while the electron-phonon scattering is dominated by layer symmetric flexural phonons in the small-angle limit, at large angles, in contrast, it is the layer antisymmetric flexural mode that is most important. We examine the role of a layer perpendicular electric field finding that it affects the conductivity strongly at low temperatures, whereas this effect is washed out by Fermi smearing at room temperatures.