scholarly journals Band structure and insulating states driven by Coulomb interaction in twisted bilayer graphene

2020 ◽  
Vol 102 (4) ◽  
Author(s):  
Tommaso Cea ◽  
Francisco Guinea
Keyword(s):  
Band Structure ◽  
Coulomb Interaction ◽  
Bilayer Graphene ◽  
Twisted Bilayer Graphene

scholarly journals Coulomb interaction, phonons, and superconductivity in twisted bilayer graphene

2021 ◽  
Vol 118 (32) ◽  
pp. e2107874118
Author(s):  
Tommaso Cea ◽  
Francisco Guinea
Keyword(s):  
Fermi Surface ◽  
Coulomb Interaction ◽  
Crucial Role ◽  
Bilayer Graphene ◽  
Combined Effect ◽  
Large Momentum ◽  
Superconducting Gap ◽  
Cooper Pairs ◽  
Electron Hole ◽  
Twisted Bilayer Graphene

The polarizability of twisted bilayer graphene, due to the combined effect of electron–hole pairs, plasmons, and acoustic phonons, is analyzed. The screened Coulomb interaction allows for the formation of Cooper pairs and superconductivity in a significant range of twist angles and fillings. The tendency toward superconductivity is enhanced by the coupling between longitudinal phonons and electron–hole pairs. Scattering processes involving large momentum transfers, Umklapp processes, play a crucial role in the formation of Cooper pairs. The magnitude of the superconducting gap changes among the different pockets of the Fermi surface.

scholarly journals Electronic properties of twisted bilayer graphene in high-energy k ⋅p-Hamiltonian approximation

2020 ◽  
Vol 34 (19n20) ◽  
pp. 2040055
Author(s):  
H. V. Grushevskaya ◽  
G. G. Krylov ◽  
H.-Y. Choi ◽  
S. P. Kruchinin
Keyword(s):  
Band Structure ◽  
Rotation Angle ◽  
Energy Gap ◽  
High Energy ◽  
Bilayer Graphene ◽  
Monolayer Graphene ◽  
Abelian Gauge ◽  
Relativistic Approach ◽  
Energy Formula ◽  
Twisted Bilayer Graphene

A model of twisted bilayer graphene has been offered on the base of developed quasi-relativistic approach with high energy [Formula: see text]-Hamiltonian. Monolayer-graphene twist is accounted as a perturbation of monolayer-graphene Hamiltonian in such a way that at a given point of the Brillouin zone there exists an external non-Abelian gauge field of another monolayer. Majorana-like resonances have been revealed in the band structure of model at a magic rotation angle [Formula: see text]. The simulations have also shown that a superlattice energy gap existing at a rotation angle [Formula: see text] vanishes at a rotation angle [Formula: see text].

scholarly journals Band structure of twisted bilayer graphene on hexagonal boron nitride

2020 ◽  
Vol 102 (15) ◽  
Author(s):  
Tommaso Cea ◽  
Pierre A. Pantaleón ◽  
Francisco Guinea
Keyword(s):  
Boron Nitride ◽  
Band Structure ◽  
Hexagonal Boron Nitride ◽  
Bilayer Graphene ◽  
Twisted Bilayer Graphene

scholarly journals Evolution of the electronic band structure of twisted bilayer graphene upon doping

2017 ◽  
Vol 7 (1) ◽  
Author(s):  
Shengqiang Huang ◽  
Matthew Yankowitz ◽  
Kanokporn Chattrakun ◽  
Arvinder Sandhu ◽  
Brian J. LeRoy
Keyword(s):  
Band Structure ◽  
Electronic Band Structure ◽  
Bilayer Graphene ◽  
Electronic Band ◽  
Twisted Bilayer Graphene

scholarly journals Gate tunable optical absorption and band structure of twisted bilayer graphene

2019 ◽  
Vol 99 (24) ◽  
Author(s):  
Kwangnam Yu ◽  
Nguyen Van Luan ◽  
Taesoo Kim ◽  
Jiwon Jeon ◽  
Jiho Kim ◽  
...  
Keyword(s):  
Optical Absorption ◽  
Band Structure ◽  
Bilayer Graphene ◽  
Twisted Bilayer Graphene

scholarly journals Tuning electron correlation in magic-angle twisted bilayer graphene using Coulomb screening

Science ◽  
2021 ◽  
Vol 371 (6535) ◽  
pp. 1261-1265
Author(s):  
Xiaoxue Liu ◽  
Zhi Wang ◽  
K. Watanabe ◽  
T. Taniguchi ◽  
Oskar Vafek ◽  
...  
Keyword(s):  
Coulomb Interaction ◽  
Theoretical Models ◽  
Bilayer Graphene ◽  
Magic Angle ◽  
Thick Barrier ◽  
Close Proximity ◽  
Twisted Bilayer Graphene ◽  
Quantum Phenomena ◽  
The Stability ◽  
Correlated Fermions

Controlling the strength of interactions is essential for studying quantum phenomena emerging in systems of correlated fermions. We introduce a device geometry whereby magic-angle twisted bilayer graphene is placed in close proximity to a Bernal bilayer graphene, separated by a 3-nanometer-thick barrier. By using charge screening from the Bernal bilayer, the strength of electron-electron Coulomb interaction within the twisted bilayer can be continuously tuned. Transport measurements show that tuning Coulomb screening has opposite effects on the insulating and superconducting states: As Coulomb interaction is weakened by screening, the insulating states become less robust, whereas the stability of superconductivity at the optimal doping is enhanced. The results provide important constraints on theoretical models for understanding the mechanism of superconductivity in magic-angle twisted bilayer graphene.

scholarly journals Superconductivity, correlated insulators, and Wess–Zumino–Witten terms in twisted bilayer graphene

2020 ◽  
Vol 117 (47) ◽  
pp. 29543-29554
Author(s):  
Maine Christos ◽  
Subir Sachdev ◽  
Mathias S. Scheurer
Keyword(s):  
High Temperature ◽  
Low Temperature ◽  
Band Structure ◽  
Symmetry Breaking ◽  
Bilayer Graphene ◽  
Flavor Symmetry ◽  
Dirac Fermions ◽  
Parent State ◽  
Comprehensive Listing ◽  
Twisted Bilayer Graphene

Recent experiments on twisted bilayer graphene have shown a high-temperature parent state with massless Dirac fermions and broken electronic flavor symmetry; superconductivity and correlated insulators emerge from this parent state at lower temperatures. We propose that the superconducting and correlated insulating orders are connected by Wess–Zumino–Witten terms, so that defects of one order contain quanta of another order and skyrmion fluctuations of the correlated insulator are a “mechanism” for superconductivity. We present a comprehensive listing of plausible low-temperature orders and the parent flavor symmetry-breaking orders. The previously characterized topological nature of the band structure of twisted bilayer graphene plays an important role in this analysis.

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