scholarly journals Strongly correlated Chern insulators in magic-angle twisted bilayer graphene

Nature ◽  
2020 ◽  
Vol 588 (7839) ◽  
pp. 610-615
Author(s):  
Kevin P. Nuckolls ◽  
Myungchul Oh ◽  
Dillon Wong ◽  
Biao Lian ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Bilayer Graphene ◽  
Magic Angle ◽  
Strongly Correlated ◽  
Chern Insulators ◽  
Twisted Bilayer Graphene

scholarly journals Correlated insulating and superconducting states in twisted bilayer graphene below the magic angle

2019 ◽  
Vol 5 (9) ◽  
pp. eaaw9770 ◽  
Author(s):  
Emilio Codecido ◽  
Qiyue Wang ◽  
Ryan Koester ◽  
Shi Che ◽  
Haidong Tian ◽  
...  
Keyword(s):  
Energy Gap ◽  
Twist Angle ◽  
High Energy ◽  
Bilayer Graphene ◽  
Unit Cell ◽  
Flat Band ◽  
Magic Angle ◽  
Strongly Correlated ◽  
New Information ◽  
Twisted Bilayer Graphene

The emergence of flat bands and correlated behaviors in “magic angle” twisted bilayer graphene (tBLG) has sparked tremendous interest, though its many aspects are under intense debate. Here we report observation of both superconductivity and the Mott-like insulating state in a tBLG device with a twist angle of ~0.93°, which is smaller than the magic angle by 15%. At an electron concentration of ±5 electrons/moiré unit cell, we observe a narrow resistance peak with an activation energy gap ~0.1 meV. This indicates additional correlated insulating state, and is consistent with theory predicting a high-energy flat band. At doping of ±12 electrons/moiré unit cell we observe resistance peaks arising from the Dirac points in the spectrum. Our results reveal that the “magic” range of tBLG is in fact larger than what is previously expected, and provide a wealth of new information to help decipher the strongly correlated phenomena observed in tBLG.

scholarly journals Unconventional sequence of correlated Chern insulators in magic-angle twisted bilayer graphene

2021 ◽  
Author(s):  
Andrew T. Pierce ◽  
Yonglong Xie ◽  
Jeong Min Park ◽  
Eslam Khalaf ◽  
Seung Hwan Lee ◽  
...  
Keyword(s):  
Bilayer Graphene ◽  
Magic Angle ◽  
Chern Insulators ◽  
Twisted Bilayer Graphene

scholarly journals Competing zero-field Chern insulators in Superconducting Twisted Bilayer Graphene

2021 ◽  
Author(s):  
Dmitri Efetov ◽  
Petr Stepanov ◽  
Ming Xie ◽  
Takashi Taniguchi ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Bilayer Graphene ◽  
Chern Number ◽  
Zero Magnetic Field ◽  
Magic Angle ◽  
Zero Field ◽  
Superconducting Phases ◽  
Chern Insulators ◽  
Twisted Bilayer Graphene ◽  
The Creation

Abstract The discovery of magic angle twisted bilayer graphene (MATBG) has unveiled a rich variety of superconducting, magnetic and topologically nontrivial phases. The existence of all these phases in one material, and their tunability, has opened new pathways for the creation of unusual gate tunable junctions. However, the required conditions for their creation – gate induced transitions between phases in zero magnetic field – have so far not been achieved. Here, we report on the first experimental demonstration of a device that is both a zero-field Chern insulator and a superconductor. The Chern insulator occurs near moiré cell filling factor = +1 in a hBN non-aligned MATBG device and manifests itself via an anomalous Hall effect. The insulator has Chern number C= ±1 and a relatively high Curie temperature of Tc ≈ 4.5 K. Gate tuning away from this state exposes strong superconducting phases with critical temperatures of up to Tc ≈ 3.5 K. In a perpendicular magnetic field above B > 0.5 T we observe a transition of the = +1 Chern insulator from Chern number C = ±1 to C = 3, characterized by a quantized Hall plateau with Ryx = h/3e2. These observations show that interaction-induced symmetry breaking in MATBG leads to zero-field ground states that include almost degenerate and closely competing Chern insulators, and that states with larger Chern numbers couple most strongly to the B-field. By providing the first demonstration of a system that allows gate-induced transitions between magnetic and superconducting phases, our observations mark a major milestone in the creation of a new generation of quantum electronics.

scholarly journals Chern insulators, van Hove singularities and topological flat bands in magic-angle twisted bilayer graphene

2021 ◽  
Vol 20 (4) ◽  
pp. 488-494 ◽  
Author(s):  
Shuang Wu ◽  
Zhenyuan Zhang ◽  
K. Watanabe ◽  
T. Taniguchi ◽  
Eva Y. Andrei
Keyword(s):  
Bilayer Graphene ◽  
Magic Angle ◽  
Van Hove Singularities ◽  
Flat Bands ◽  
Chern Insulators ◽  
Twisted Bilayer Graphene

scholarly journals Gate-defined Josephson junctions in magic-angle twisted bilayer graphene

2021 ◽  
Author(s):  
Folkert K. de Vries ◽  
Elías Portolés ◽  
Giulia Zheng ◽  
Takashi Taniguchi ◽  
Kenji Watanabe ◽  
...  
Keyword(s):  
Josephson Junctions ◽  
Bilayer Graphene ◽  
Magic Angle ◽  
Twisted Bilayer Graphene

Raman spectra of twisted bilayer graphene close to the magic angle

2D Materials ◽  
2022 ◽  
Author(s):  
Tiago Campolina Barbosa ◽  
Andreij C. Gadelha ◽  
Douglas A. A. Ohlberg ◽  
Kenji Watanabe ◽  
Takashi Taniguchi ◽  
...  
Keyword(s):  
Raman Spectra ◽  
Laser Excitation ◽  
Bilayer Graphene ◽  
Geometrical Model ◽  
Excitation Wavelength ◽  
Magic Angle ◽  
Phonon Interaction ◽  
Electron Phonon Interaction ◽  
Excitation Laser ◽  
Twisted Bilayer Graphene

Abstract In this work, we study the Raman spectra of twisted bilayer graphene samples as a function of their twist-angles (θ), ranging from 0.03º to 3.40º, where local θ are determined by analysis of their associated moiré superlattices, as imaged by scanning microwave impedance microscopy. Three standard excitation laser lines are used (457, 532, and 633 nm wavelengths), and the main Raman active graphene bands (G and 2D) are considered. Our results reveal that electron-phonon interaction influences the G band's linewidth close to the magic angle regardless of laser excitation wavelength. Also, the 2D band lineshape in the θ < 1º regime is dictated by crystal lattice and depends on both the Bernal (AB and BA) stacking bilayer graphene and strain soliton regions (SP) [1]. We propose a geometrical model to explain the 2D lineshape variations, and from it, we estimate the SP width when moving towards the magic angle.

scholarly journals Charge order and broken rotational symmetry in magic-angle twisted bilayer graphene

Nature ◽  
2019 ◽  
Vol 573 (7772) ◽  
pp. 91-95 ◽  
Author(s):  
Yuhang Jiang ◽  
Xinyuan Lai ◽  
Kenji Watanabe ◽  
Takashi Taniguchi ◽  
Kristjan Haule ◽  
...  
Keyword(s):  
Rotational Symmetry ◽  
Charge Order ◽  
Bilayer Graphene ◽  
Magic Angle ◽  
Twisted Bilayer Graphene
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