• 文献标题:   Moire Flat Bands in Twisted Double Bilayer Graphene
  • 文献类型:   Article
  • 作  者:   HADDADI F, WU QS, KRUCHKOV AJ, YAZYEV OV
  • 作者关键词:   twisted double bilayer graphene, moire superlattice, magic angle, flat band, polarization, crystal field
  • 出版物名称:   NANO LETTERS
  • ISSN:   1530-6984 EI 1530-6992
  • 通讯作者地址:   Ecole Polytech Fed Lausanne
  • 被引频次:   15
  • DOI:   10.1021/acs.nanolett.9b05117
  • 出版年:   2020

▎ 摘  要

We investigate twisted double bilayer graphene (TDBG), a four-layer system composed of two AB-stacked graphene bilayers rotated with respect to each other by a small angle. Our ab initio band structure calculations reveal a considerable energy gap at the charge-neutrality point that we assign to the intrinsic symmetric polarization (ISP). We then introduce the ISP effect into the tight-binding parametrization and perform calculations on TDBG models that include lattice relaxation effects down to very small twist angles. We identify a narrow region around the magic angle characterized by a manifold of remarkably flat bands gapped out from other states even without external electric fields. To understand the fundamental origin of the magic angle in TDBG, we construct a continuum model that points to a hidden mathematical link to the twisted bilayer graphene model, thus indicating that the band flattening is a fundamental feature of TDBG and is not a result of external fields.