Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice

Chen, Guorui; Jiang, Lili; Wu, Shuang; Lyu, Bosai; Li, Hongyuan; Chittari, Bheema Lingam; Watanabe, Kenji; Taniguchi, Takashi; Shi, Zhiwen; Jung, Jeil; Zhang, Yuanbo; Wang, Feng

doi:10.1038/s41567-018-0387-2

Cited by 612 publications

(518 citation statements)

References 29 publications

(68 reference statements)

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“…Most saliently, we provide microscopic evidence that high temperature fractional Chern insulators can form in twisted bilayer graphene aligned with hexagonal boron nitride.Setup. Motived by the recent discoveries [11][12][13]15] along with theoretical predictions [16,21] of spin and valley polarized insulators at integer fillings in various Moiré bands, we consider electrons with polarized spin arXiv:1912.04907v1 [cond-mat.mes-hall]…”

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confidence: 99%

“…A related platform for studying correlated physics is the Moiré superlattice formed when trilayer graphene is aligned with boron nitride. Unlike magic angle twisted bilayer graphene, the bandwidth and the topology of the minibands can be controlled by the strength of the applied displacement field resulting in gate-tunable Mott insulating and superconducting states [13,14]. Also in this case, a correlated ferromagnetic Chern insulator has been reported at a filling corresponding to one hole per Moiré unit cell [15].…”

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confidence: 99%

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Particle-Hole Duality, Emergent Fermi Liquids, and Fractional Chern Insulators in Moiré Flatbands

2020

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Moiré flatbands, occurring e.g. in twisted bilayer graphene at magic angles, have attracted ample interest due to their high degree of experimental tunability and the intriguing possibility of generating novel strongly interacting phases. Here we consider the core problem of Coulomb interactions within fractionally filled spin and valley polarized Moiré flatbands and demonstrate that the dual description in terms of holes, which acquire a non-trivial hole-dispersion, provides key physical intuition and enables the use of standard perturbative techniques for this strongly correlated problem. In experimentally relevant examples such as ABC stacked trilayer and twisted bilayer graphene aligned with boron nitride, it leads to emergent interaction-driven Fermi liquid states at electronic filling fractions down to around 1/3 and 2/3 respectively. At even lower filling fractions, the electron density still faithfully tracks the single-hole dispersion while exhibiting distinct non-Fermi liquid behavior. Most saliently, we provide microscopic evidence that high temperature fractional Chern insulators can form in twisted bilayer graphene aligned with hexagonal boron nitride.Setup. Motived by the recent discoveries [11][12][13]15] along with theoretical predictions [16,21] of spin and valley polarized insulators at integer fillings in various Moiré bands, we consider electrons with polarized spin arXiv:1912.04907v1 [cond-mat.mes-hall]

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Particle-Hole Duality, Emergent Fermi Liquids, and Fractional Chern Insulators in Moiré Flatbands

2020

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“…Recent experimental progress in 2D moiré superlattices such as twisted bilayer graphene [14][15][16][17] and graphene heterostructures [18][19][20][21] has enabled us to continuously tune electronic band structures in 2D systems, where high-order VHS can be realized at symmetric points [13] or generic positions [22], and could be relevant to experimentally observed insulating and superconducting phases at magic angle [14][15][16].…”

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Classification of critical points in energy bands based on topology, scaling, and symmetry

Yuan

2020

Phys. Rev. B

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A critical point of the energy dispersion is the momentum where electron velocity vanishes. At the corresponding energy, the density of states (DOS) exhibits non-analyticity such as divergence. Critical points can be first classified as ordinary and high-order ones, and the ordinary critical points have been studied thoroughly by Léon van Hove. In this work, we describe and classify high-order critical points based on topology, scaling and symmetry, which are beyond Léon van Hove's framework. We show that high-order critical points can have power-law divergent DOS with particle-hole asymmetry, and can be realized at generic or symmetric momenta by tuning a few parameters such as twist angle, strain, pressure and/or external fields.

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“…A prime example is twisted bilayer graphene (tBLG) [32][33][34][35], where the lowest two bands carry a fragile topology [36][37][38][39][40] and become flat near the magic twist angle θ ≈ 1.1 • . In addition, flat valley Chern bands can be realized in tBLG with aligned hBN substrate [41][42][43], twisted double bilayer graphene [44][45][46], ABC trilayer graphene on hBN [47][48][49] and twisted bilayer transition metal dichalcogenides [50,51], etc. The small bandwidths make electron-electron interactions important [52][53][54][55][56][57][58][59], and further lead to intriguing interacting phases in experiments including superconductivity, correlated insulator and QAH effect.So far, all of the experimental Moiré systems are timereversal (TR) invariant at the single particle level, thus the total Chern number always equals to zero.…”

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Flat Chern Band from Twisted Bilayer MnBi2Te4

et al. 2020

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We construct a continuum model for the Moiré superlattice of twisted bilayer MnBi2Te4, and study the band structure of the bilayer in both ferromagnetic (FM) and antiferromagnetic (AFM) phases. We find the system exhibits highly tunable Chern bands with Chern number up to 3. We show that a twist angle of 1 • turns the highest valence band into a flat band with Chern number ±1 that is isolated from all other bands in both FM and AFM phases. This result provides a promising platform for realizing time-reversal breaking correlated topological phases, such as fractional Chern insulator and p + ip topological superconductor. In addition, our calculation indicates that the twisted stacking facilitates the emergence of quantum anomalous Hall effect in MnBi2Te4.Topology has become one of the central topics in condensed matter physics. The discovery of topological insulator (TI) [1][2][3][4][5][6][7][8][9][10][11], quantum anomalous Hall (QAH) effect [12][13][14][15][16][17][18] and other topological states have significantly enriched the variety of quantum matter, and may lead to potential applications in electronics and quantum computation [19][20][21][22][23]. Electron-electron interaction plays an essential role in fractional quantum Hall effect, and there have been proposals of strongly correlated topological states such as fractional TI and fractional Chern insulator (FCI) without magnetic field [24][25][26][27][28][29][30][31]. Experimentally realizing such states is, however, challenging because flat topological electronic bands are generally required for electron-electron interactions to manifest.Recently, it is shown that Moiré superlattices in twisted or lattice mismatched two-dimensional (2D) materials can give rise to flat topological bands. A prime example is twisted bilayer graphene (tBLG) [32][33][34][35], where the lowest two bands carry a fragile topology [36][37][38][39][40] and become flat near the magic twist angle θ ≈ 1.1 • . In addition, flat valley Chern bands can be realized in tBLG with aligned hBN substrate [41][42][43], twisted double bilayer graphene [44][45][46], ABC trilayer graphene on hBN [47][48][49] and twisted bilayer transition metal dichalcogenides [50,51], etc. The small bandwidths make electron-electron interactions important [52][53][54][55][56][57][58][59], and further lead to intriguing interacting phases in experiments including superconductivity, correlated insulator and QAH effect.So far, all of the experimental Moiré systems are timereversal (TR) invariant at the single particle level, thus the total Chern number always equals to zero. Therefore, even with flat bands, it is difficult to achieve TR breaking interacting topological states such as the FCI in these systems. This motivates us to consider the Moiré superlattice of TR breaking layered materials. A promising system is 3D antiferromagnetic (AFM) topological axion insulator MnBi 2 Te 4 [60-77], which can be driven into a ferromagnetic (FM) Weyl semimetal or 3D QAH insulator. The material consists of Van der Waals coupl...

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Evidence of a gate-tunable Mott insulator in a trilayer graphene moiré superlattice

Cited by 612 publications

References 29 publications

Particle-Hole Duality, Emergent Fermi Liquids, and Fractional Chern Insulators in Moiré Flatbands

Particle-Hole Duality, Emergent Fermi Liquids, and Fractional Chern Insulators in Moiré Flatbands

Classification of critical points in energy bands based on topology, scaling, and symmetry

Flat Chern Band from Twisted Bilayer MnBi2Te4

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