Localization of lattice dynamics in low-angle twisted bilayer graphene

Andreij C. Gadelha, Douglas A. A. Ohlberg, Cassiano Rabelo, Eliel G. S. Neto, Thiago L. Vasconcelos, João L. Campos, Jessica S. Lemos, Vinícius Ornelas, Daniel Miranda, Rafael Nadas, Fabiano C. Santana, Kenji Watanabe, Takashi Taniguchi, Benoit Troeye, Michael Lamparski, Vincent Meunier (), Viet-Hung Nguyen, Dawid Paszko, Jean-Christophe Charlier, Leonardo C. Campos, Luiz G. Cançado, Gilberto Medeiros-Ribeiro and Ado Jorio ()
Additional contact information
Andreij C. Gadelha: Universidade Federal de Minas Gerais
Douglas A. A. Ohlberg: Universidade Federal de Minas Gerais
Cassiano Rabelo: Universidade Federal de Minas Gerais
Eliel G. S. Neto: Universidade Federal da Bahia, Campus Universitário de Ondina
Thiago L. Vasconcelos: Divisão de Metrologia de Materiais, Inmetro
João L. Campos: Universidade Federal de Minas Gerais
Jessica S. Lemos: Universidade Federal de Minas Gerais
Vinícius Ornelas: Universidade Federal de Minas Gerais
Daniel Miranda: Universidade Federal de Minas Gerais
Rafael Nadas: Universidade Federal de Minas Gerais
Fabiano C. Santana: Universidade Federal de Minas Gerais
Kenji Watanabe: National Institute for Materials Science
Takashi Taniguchi: National Institute for Materials Science
Benoit Troeye: Jonsson Rowland Science Center
Michael Lamparski: Jonsson Rowland Science Center
Vincent Meunier: Jonsson Rowland Science Center
Viet-Hung Nguyen: Université Catholique de Louvain
Dawid Paszko: Université Catholique de Louvain
Jean-Christophe Charlier: Université Catholique de Louvain
Leonardo C. Campos: Universidade Federal de Minas Gerais
Luiz G. Cançado: Universidade Federal de Minas Gerais
Gilberto Medeiros-Ribeiro: Universidade Federal de Minas Gerais
Ado Jorio: Universidade Federal de Minas Gerais

Nature, 2021, vol. 590, issue 7846, 405-409

Abstract: Abstract Twisted bilayer graphene is created by slightly rotating the two crystal networks in bilayer graphene with respect to each other. For small twist angles, the material undergoes a self-organized lattice reconstruction, leading to the formation of a periodically repeated domain1–3. The resulting superlattice modulates the vibrational3,4 and electronic5,6 structures within the material, leading to changes in the behaviour of electron–phonon coupling7,8 and to the observation of strong correlations and superconductivity9. However, accessing these modulations and understanding the related effects are challenging, because the modulations are too small for experimental techniques to accurately resolve the relevant energy levels and too large for theoretical models to properly describe the localized effects. Here we report hyperspectral optical images, generated by a nano-Raman spectroscope10, of the crystal superlattice in reconstructed (low-angle) twisted bilayer graphene. Observations of the crystallographic structure with visible light are made possible by the nano-Raman technique, which reveals the localization of lattice dynamics, with the presence of strain solitons and topological points1 causing detectable spectral variations. The results are rationalized by an atomistic model that enables evaluation of the local density of the electronic and vibrational states of the superlattice. This evaluation highlights the relevance of solitons and topological points for the vibrational and electronic properties of the structures, particularly for small twist angles. Our results are an important step towards understanding phonon-related effects at atomic and nanometric scales, such as Jahn–Teller effects11 and electronic Cooper pairing12–14, and may help to improve device characterization15 in the context of the rapidly developing field of twistronics16.

Date: 2021
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DOI: 10.1038/s41586-021-03252-5

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