Correlated states in twisted double bilayer graphene

By Cheng Shen, Yanbang Chu, Quansheng Wu, Na Li, Shuopei Wang, Yanchong Zhao, Jian Tang, Jieying Liu, Jinpeng Tian, Kenji Watanabe and 6 more. Nature Physics, 2019

485 citations recorded by the source corpus.

Electron–electron interactions play an important role in graphene and related systems and can induce exotic quantum states, especially in a stacked bilayer with a small twist angle 1 – 7 . For bilayer graphene where the two layers are twisted by the ‘magic angle’, flat band and strong many-body effects lead to correlated insulating states and superconductivity 4 – 7 . In contrast to monolayer graphene, the band structure of untwisted bilayer graphene can be further tuned by a displacement field 8 – 10 , providing an extra degree of freedom to control the flat band that should appear when two bilayers are stacked on top of each other. Here, we report the discovery and characterization of displacement field-tunable electronic phases in twisted double bilayer graphene. We observe insulating states at a half-filled conduction band in an intermediate range of displacement fields. Furthermore, the resistance gap in the correlated insulator increases with respect to the in-plane magnetic fields and we find that the g factor, according to the spin Zeeman effect, is ~2, indicating spin polarization at half-filling. These results establish twisted double bilayer graphene as an easily tunable platform for exploring quantum many-body states. Placing two Bernal-stacked graphene bilayers on top of each other with a small twist angle gives correlated states. As the band structure can be tuned by an electric field, this platform is a more varied setting to study correlated electrons.

Subfields: Atomic and Molecular Physics, and Optics, Materials Chemistry

View Paper: https://www.semanticscholar.org/paper/53bd707e73aad9064e5988e52336b21422a41490

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Citations in the corpus

Electrically tunable correlated and topological states in twisted monolayer–bilayer graphene (2020, background): “These features correspond closely with the CI and metallic states in tDBG [10–14], suggesting that at this twist angle the phase diagram of tMBG is similar to that of tDBG, with small differences arising owing to the absence”