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Gap Opening in Twisted Double Bilayer Graphene by Crystal Fields.

Peter Rickhaus1, Giulia Zheng1, Jose L Lado2,3

  • 1Solid State Physics Laboratory , ETH Zürich , CH-8093 Zürich , Switzerland.

Nano Letters
|November 1, 2019
PubMed
Summary

Crystal fields create an intrinsic band gap in twisted double bilayer graphene. Applying an external field closes these gaps, revealing crystal field strengths and their significant impact on electronic properties.

Keywords:
bilayer graphenecrystal fieldfield inducedgapp−n junctiontwisted

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Area of Science:

  • Condensed Matter Physics
  • Materials Science

Background:

  • Crystal fields arise from potential differences between atomic species, naturally present in van der Waals heterostructures.
  • Twisted graphene multilayers offer tunable electronic properties, but the role of crystal fields remains underexplored.

Purpose of the Study:

  • To investigate the impact of crystal fields on the electronic band structure of large-angle twisted double bilayer graphene.
  • To experimentally demonstrate and quantify the intrinsic band gap induced by crystal fields in this material.

Main Methods:

  • Experimental characterization of twisted double bilayer graphene encapsulated in hexagonal boron nitride (hBN).
  • Application of external electric fields to tune and close band gaps.
  • First-principles calculations and low-energy modeling to analyze band structure modifications.

Main Results:

  • Twisted double bilayer graphene exhibits an intrinsic band gap due to crystal fields.
  • External electric fields can close these band gaps, enabling crystal field determination.
  • Crystal fields were quantified, pointing from outer to inner layers with strengths of approximately 0.13 V/nm and 0.12 V/nm for the bottom and top bilayers, respectively.
  • Crystal fields were shown to open a band gap in the ground state.

Conclusions:

  • Crystal fields significantly modify the band structure of twisted double bilayer graphene.
  • These effects are crucial for accurately predicting the electronic properties of twisted graphene multilayers.
  • The findings highlight the importance of considering crystal fields in designing and understanding van der Waals heterostructures.