Flat bands in twisted double bilayer graphene

Narasimha Raju Chebrolu, Bheema Lingam Chittari, and Jeil Jung
Phys. Rev. B 99, 235417 – Published 17 June 2019
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Abstract

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 θ and interlayer coupling ω, 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 θ1.05 to larger values of up to θ1.5 when P2.5 GPa, where θω/υF. 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 or 180 alignments.

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  • Received 24 January 2019
  • Revised 24 April 2019

DOI:https://doi.org/10.1103/PhysRevB.99.235417

©2019 American Physical Society

Physics Subject Headings (PhySH)

Condensed Matter, Materials & Applied Physics

Authors & Affiliations

Narasimha Raju Chebrolu, Bheema Lingam Chittari, and Jeil Jung*

  • Department of Physics, University of Seoul, Seoul 02504, Korea

  • *jeiljung@uos.ac.kr

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Issue

Vol. 99, Iss. 23 — 15 June 2019

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