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arXiv · 2006.14000

Emergent Symmetry and Valley Chern Insulator in Twisted Double-Bilayer Graphene

Yimeng Wang·G. William Burg·Biao Lian·Kenji Watanabe·Takashi Taniguchi·B. Andrei Bernevig·Emanuel Tutuc
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Abstract

Theoretical calculations show that twisted double bilayer graphene (TDBG) under a transverse electric field develops a valley Chern number 2 at charge neutrality. Using thermodynamic and thermal activation measurements we report the experimental observation of a universal closing of the charge neutrality gap in the Hofstadter spectrum of TDBG at 1/2 magnetic flux per unit cell, in agreement with theoretical predictions for a valley Chern number 2 gap. Our theoretical analysis of the experimental data shows that the interaction energy, while larger than the flat-band bandwidth in TDBG near 1\deg does not alter the emergent valley symmetry or the single-particle band topology.

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Yimeng Wang, G. William Burg, Biao Lian, Kenji Watanabe, Takashi Taniguchi, B. Andrei Bernevig, Emanuel Tutuc. 2020-06-24. Emergent Symmetry and Valley Chern Insulator in Twisted Double-Bilayer Graphene. https://doi.org/10.1103/physrevlett.133.246401

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