Interaction-driven band flattening and correlated phases in twisted bilayer graphene

Choi, Youngjoon; Kim, Hyunjin; Lewandowski, Cyprian; Peng, Yang; Thomson, Alex; Polski, Robert; Zhang, Yiran; Watanabe, Kenji; Taniguchi, Takashi; Alicea, Jason; Nadj-Perge, Stevan

doi:10.1038/s41567-021-01359-0

Cited by 43 publications

(41 citation statements)

References 43 publications

(73 reference statements)

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“…Twisted bilayer graphene (TBG) shows a complex phase diagram, which combines superconducting and insulating phases [1,2], and resembles strongly correlated materials previously encountered in condensed matter physics [3][4][5][6]. On the other hand, superconductivity seems more prevalent in TBG [7][8][9][10][11], while in other strongly correlated materials magnetic phases are dominant.…”

Section: Introductionmentioning

confidence: 95%

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

Cea,

Guinea

2021

Preprint

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Section: Introductionmentioning

confidence: 95%

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

Cea,

Guinea

2021

Preprint

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“…4e. Our scenario relies on the fact that strong interactions can heavily deform the TBG bands, such that the Γ point of the mini-Brillouin zone can be inverted, as reported by local spectroscopy measurements 40 .…”

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confidence: 97%

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Polski¹,

Zhang²,

Yang³

et al. 2022

Preprint

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Twisted bilayer graphene (TBG) near the magic twist angle of ∼1.1°exhibits a rich phase diagram.However, the interplay between different phases and their dependence on twist angle is still elusive.Here, we explore the stability of various TBG phases and demonstrate that superconductivity near filling of two electrons per moiré unit cell alongside Fermi surface reconstructions, as well as entropydriven high-temperature phase transitions and linear-in-T resistance occur over a range of twist angles which extends far beyond those exhibiting correlated insulating phases. In the vicinity of the magic angle, we also find a metallic phase that displays a hysteretic anomalous Hall effect and incipient Chern insulating behaviour. Such a metallic phase can be rationalized in terms of the interplay between interaction-driven deformations of TBG bands leading to Berry curvature redistribution and Fermi surface reconstruction. Our results provide an extensive perspective on the hierarchy of correlated phases in TBG as classified by their robustness against deviations from the magic angle or, equivalently, their electronic interaction requirements. TBG is a highly tunable platform for exploring the effects of strong electronic interactions and topological bands [1][2][3][4][5][6][7][8][9] . At the magic angle, i.e., when the strength of the interactions among electrons is maximized relative to their kinetic energy, pronounced signatures of correlated phases emerge 1,2,10 . Away from the magic angle, the effective interaction strength is reduced and the correlated phases are believed to disappear rapidly. However, despite the strong impact of the twist angle on the phase diagram of nearly-magic TBG, this dependence is still experimentally under-explored. Here we report systematic measurements on multiple devices covering a wide range of twist angles between 0.79°and 1.23°(see Supplementary Table I for an overview) and examine the overall impact of twist angle, and thus strength of interactions, on the phase

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“…4(e), leading to a strong peak in ⇧ KK around (n1, n2) = (1,25). Since k4 k9 ⇡ k17 k22 ⇡ k1 k25, ⇧ ph KK also exhibits peaks around (n1, n2) = (9, 4) and (17,22) as marked in Fig. 4(d) which impact intra Fermi surface pairing interactions.…”

Section: P X I 5 H T + W P N 8 a U U H J B 8 = < / L A T E X I T > < ...mentioning

confidence: 95%

“…KK also exhibits peaks around (n 1 , n 2 ) = (9, 4) and (17,22) as marked in Fig. 4(d) which impact intra-Fermi surface pairing interactions.…”

Section: (B)-(c)mentioning

confidence: 97%

“…Introduction-Because of their exceptional mechanical properties and weak interlayer bonding, graphene multilayers have long been recognized as an attractive system for the fabrication of two-dimensional material devices that are nearly perfectly free from unintended imperfections. Recent experiments [1][2][3][4][5][6][7][8][9][10][11][12][13][14][15][16][17][18] have demonstrated that graphene multilayers can also exhibit rich strong-correlation physics, including broken spin/valley flavor symmetries and superconductivity, when the layers are twisted to magic relative orientation angles that yield extremely flat moiré superlattice bands [19][20][21][22][23]. Twists come with challenges, however, because twist angle changes during processing make systematic studies more difficult, and because devices inevitably have some twist-angle disorder [24].…”

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confidence: 99%

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Functional Renormalization Group Study of Superconductivity in Rhombohedral Trilayer Graphene

Wei¹,

Huang²,

Wolf³

et al. 2022

Preprint

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We employ a functional renormalization group approach to ascertain the pairing mechanism and symmetry in the recently observed superconducting phase of rhombohedral trilayer graphene. Superconductivity in this system occurs in a regime of carrier density and displacement field with a weakly distorted annular Fermi sea. We find that repulsive Coulomb interactions can induce electron pairing on the Fermi surface by taking advantage of momentum-space structure associated with its finite width. The degeneracy between spin-singlet and spin-triplet pairing is lifted by valleyexchange interactions that strengthen under the RG flow and develop nontrivial momentum-space structures. In our calculation, the inner and outer Fermi surfaces prefer d-wave spin-singlet and p-wave spin-triplet pairings, respectively. We predict that a transition from the spin-singlet pairing observed at present to spin-triplet pairing will occur when the electrical gates of the device are positioned further from the dielectric encapsulated trilayer.

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Interaction-driven band flattening and correlated phases in twisted bilayer graphene

Cited by 43 publications

References 43 publications

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

Hierarchy of Symmetry Breaking Correlated Phases in Twisted Bilayer Graphene

Functional Renormalization Group Study of Superconductivity in Rhombohedral Trilayer Graphene

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