Emerging flat bands in large-angle twisted bi-layer graphene under pressures

Nanoscale ◽  
2021 ◽  
Author(s):  
Liangbing Ge ◽  
Ni Kun ◽  
Xiaojun Wu ◽  
Zhengping Fu ◽  
Yalin Lu ◽  
...  
Keyword(s):  
Large Angle ◽  
Magic Angle ◽  
Unconventional Superconductivity ◽  
Flat Bands ◽  
Layer Graphene

Recent experiments on magic-angle twisted bi-layer graphene have attracted an intensive attention due to exotic properties such as unconventional superconductivity and correlated insulation. These phenomena were often found at a...

scholarly journals Theory of correlated insulating behaviour and spin-triplet superconductivity in twisted double bilayer graphene

2019 ◽  
Vol 10 (1) ◽  
Author(s):  
Jong Yeon Lee ◽  
Eslam Khalaf ◽  
Shang Liu ◽  
Xiaomeng Liu ◽  
Zeyu Hao ◽  
...  
Keyword(s):  
Displacement Field ◽  
Twist Angle ◽  
Vertical Displacement ◽  
Bilayer Graphene ◽  
Magic Angle ◽  
Hartree Fock ◽  
Flat Bands ◽  
Half Filling ◽  
Spin Triplet ◽  
Experimental Findings

AbstractTwo graphene monolayers twisted by a small magic angle exhibit nearly flat bands, leading to correlated electronic states. Here we study a related but different system with reduced symmetry - twisted double bilayer graphene (TDBG), consisting of two Bernal stacked bilayer graphenes, twisted with respect to one another. Unlike the monolayer case, we show that isolated flat bands only appear on application of a vertical displacement field. We construct a phase diagram as a function of twist angle and displacement field, incorporating interactions via a Hartree-Fock approximation. At half-filling, ferromagnetic insulators are stabilized with valley Chern number $${C}_{{\rm{v}}}=\pm 2$$Cv=±2. Upon doping, ferromagnetic fluctuations are argued to lead to spin-triplet superconductivity from pairing between opposite valleys. We highlight a novel orbital effect arising from in-plane fields plays an important role in interpreting experiments. Combined with recent experimental findings, our results establish TDBG as a tunable platform to realize rare phases in conventional solids.

scholarly journals Flat Bands in Magic-Angle Vibrating Plates

2020 ◽  
Vol 125 (21) ◽  
Author(s):  
María Rosendo López ◽  
Fernando Peñaranda ◽  
Johan Christensen ◽  
Pablo San-Jose
Keyword(s):  
Magic Angle ◽  
Flat Bands ◽  
Vibrating Plates

scholarly journals Unconventional superconductivity in magic-angle graphene superlattices

Nature ◽  
2018 ◽  
Vol 556 (7699) ◽  
pp. 43-50 ◽  
Author(s):  
Yuan Cao ◽  
Valla Fatemi ◽  
Shiang Fang ◽  
Kenji Watanabe ◽  
Takashi Taniguchi ◽  
...  
Keyword(s):  
Magic Angle ◽  
Unconventional Superconductivity

Full-Spectrum Thermal Analysis in Twisted Bilayer Graphene

2021 ◽  
Author(s):  
Wenxiang Liu ◽  
Yongqiang Wu ◽  
Yang Hong ◽  
Bo Hou ◽  
Jingchao Zhang ◽  
...  
Keyword(s):  
Thermal Analysis ◽  
Bilayer Graphene ◽  
Magic Angle ◽  
Unconventional Superconductivity ◽  
Full Spectrum ◽  
Twisted Bilayer Graphene ◽  
Twisting Angle

It was recently reported that a magic angle, i.e. 1.1º, exists in twisted bilayer graphene which could lead to intrinsic unconventional superconductivity. Variations of the twisting angle between different graphene...

scholarly journals Flat Bands in Magic-Angle Bilayer Photonic Crystals at Small Twists

2021 ◽  
Vol 126 (22) ◽  
Author(s):  
Kaichen Dong ◽  
Tiancheng Zhang ◽  
Jiachen Li ◽  
Qingjun Wang ◽  
Fuyi Yang ◽  
...  
Keyword(s):  
Photonic Crystals ◽  
Magic Angle ◽  
Flat Bands

scholarly journals Observation of a flat band and bandgap in millimeter-scale twisted bilayer graphene

2021 ◽  
Vol 2 (1) ◽  
Author(s):  
Keiju Sato ◽  
Naoki Hayashi ◽  
Takahiro Ito ◽  
Noriyuki Masago ◽  
Makoto Takamura ◽  
...  
Keyword(s):  
Large Angle ◽  
Bilayer Graphene ◽  
Epitaxial Graphene ◽  
Photoemission Spectroscopy ◽  
Flat Band ◽  
Magic Angle ◽  
Graphene Layers ◽  
Angle Resolved Photoemission Spectroscopy ◽  
Twisted Bilayer Graphene ◽  
Micrometer Scale

AbstractMagic-angle twisted bilayer graphene, consisting of two graphene layers stacked at a special angle, exhibits superconductivity due to the maximized density of states at the energy of the flat band. Generally, experiments on twisted bilayer graphene have been performed using micrometer-scale samples. Here we report the fabrication of twisted bilayer graphene with an area exceeding 3 × 5 mm2 by transferring epitaxial graphene onto another epitaxial graphene, and observation of a flat band and large bandgap using angle-resolved photoemission spectroscopy. Our results suggest that the substrate potential induces both the asymmetrical doping in large angle twisted bilayer graphene and the electron doped nature of the flat band in magic-angle twisted bilayer graphene.

scholarly journals Flat bands, electron interactions, and magnetic order in magic-angle mono-trilayer graphene

2021 ◽  
Vol 5 (8) ◽  
Author(s):  
Zachary A. H. Goodwin ◽  
Lennart Klebl ◽  
Valerio Vitale ◽  
Xia Liang ◽  
Vivek Gogtay ◽  
...  
Keyword(s):  
Magnetic Order ◽  
Magic Angle ◽  
Flat Bands ◽  
Trilayer Graphene ◽  
Electron Interactions

scholarly journals Multiple flat bands and topological Hofstadter butterfly in twisted bilayer graphene close to the second magic angle

2021 ◽  
Vol 118 (30) ◽  
pp. e2100006118
Author(s):  
Xiaobo Lu ◽  
Biao Lian ◽  
Gaurav Chaudhary ◽  
Benjamin A. Piot ◽  
Giulio Romagnoli ◽  
...  
Keyword(s):  
Condensed Matter ◽  
Bilayer Graphene ◽  
Band Gaps ◽  
Magic Angle ◽  
Two Dimensional ◽  
Quantum Phases ◽  
Electron Band ◽  
Flat Bands ◽  
Twisted Bilayer Graphene ◽  
Hofstadter Butterfly

Moiré superlattices in two-dimensional van der Waals heterostructures provide an efficient way to engineer electron band properties. The recent discovery of exotic quantum phases and their interplay in twisted bilayer graphene (tBLG) has made this moiré system one of the most renowned condensed matter platforms. So far studies of tBLG have been mostly focused on the lowest two flat moiré bands at the first magic angle θm1 ∼ 1.1°, leaving high-order moiré bands and magic angles largely unexplored. Here we report an observation of multiple well-isolated flat moiré bands in tBLG close to the second magic angle θm2 ∼ 0.5°, which cannot be explained without considering electron–election interactions. With high magnetic field magnetotransport measurements we further reveal an energetically unbound Hofstadter butterfly spectrum in which continuously extended quantized Landau level gaps cross all trivial band gaps. The connected Hofstadter butterfly strongly evidences the topologically nontrivial textures of the multiple moiré bands. Overall, our work provides a perspective for understanding the quantum phases in tBLG and the fractal Hofstadter spectra of multiple topological bands.

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