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Flat bands in twisted double bilayer graphene

机译：双层双层石墨烯中的扁平带

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摘要

Flat bands with extremely narrow bandwidths on the order of a few millielectron volts can appear in twisted multilayer graphene systems for appropriate system parameters. Here we investigate the electronic structure of a twisted bi-bilayer graphene, or twisted double bilayer graphene, to find the parameter space where isolated flat bands can emerge as a function of twist angle, vertical pressure, and interlayer potential differences. We find that in twisted bi-bilayer graphene the bandwidth is generally flatter than in twisted bilayer graphene by roughly up to a factor of 2 in the same parameter space of twist angle theta and interlayer coupling., making it in principle simpler to tailor narrow bandwidth flat bands. Application of vertical pressure can enhance the first magic angle in minimal models at theta similar to 1.05 degrees to larger values of up to theta similar to 1.5 degrees when P similar to 2.5 GPa, where theta proportional to omegau(F). Narrow bandwidths are expected in bi-bilayers for a continuous range of small twist angles, i.e., without magic angles, when intrinsic bilayer gaps open by electric fields, or due to remote hopping terms. We find that moderate vertical electric fields can contribute in lifting the degeneracy of the low-energy flat bands by enhancing the primary gap near the Dirac point and the secondary gap with the higher energy bands. Distinct valley Chern bands are expected near 0 degrees or 180 degrees alignments.
机译：对于适当的系统参数，在多层多层石墨烯系统中可能会出现几毫伏量级的极窄带宽的平坦带。在这里，我们研究了扭曲的双层石墨烯或扭曲的双层双层石墨烯的电子结构，以找到参数空间，其中孤立的平坦带可以作为扭曲角，垂直压力和层间电势差的函数出现。我们发现，在相同的扭曲角θ和层间耦合参数空间中，双绞线双层石墨烯的带宽通常比双绞线双层石墨烯的带宽大约两倍。平带。垂直压力的施加可以在最小模型中以大约1.05度的theta增强第一个魔术角，直到当P接近2.5 GPa时，最大theta近似于1.5度的theta值，其中theta与omega / nu（F）成比例。当固有双层间隙由于电场或由于远程跳变项而打开时，对于连续的小扭转角范围（即没有魔术角），在双层中期望有较窄的带宽。我们发现，适度的垂直电场可通过增强Dirac点附近的主间隙和较高能带的次级间隙来提高低能平带的退化。预计在0度或180度对准附近有不同的谷Chern带。

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  • 来源
    《Physical review》 |2019年第23期|235417.1-235417.13|共13页
  • 作者

    Chebrolu Narasimha Raju; Chittari Bheema Lingam; Jung Jeil;

  • 作者单位

    Univ Seoul, Dept Phys, Seoul 02504, South Korea;

    Univ Seoul, Dept Phys, Seoul 02504, South Korea;

    Univ Seoul, Dept Phys, Seoul 02504, South Korea;

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