scholarly journals Electron–hole collision limited transport in charge-neutral bilayer graphene

2017 ◽  
Vol 13 (12) ◽  
pp. 1207-1214 ◽  
Author(s):  
Youngwoo Nam ◽  
Dong-Keun Ki ◽  
David Soler-Delgado ◽  
Alberto F. Morpurgo
Keyword(s):  
Bilayer Graphene ◽  
Electron Hole

scholarly journals Chemical potential and quantum Hall ferromagnetism in bilayer graphene

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 58-61 ◽  
Author(s):  
Kayoung Lee ◽  
Babak Fallahazad ◽  
Jiamin Xue ◽  
David C. Dillen ◽  
Kyounghwan Kim ◽  
...  
Keyword(s):  
Degrees Of Freedom ◽  
Chemical Potential ◽  
Hexagonal Boron Nitride ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Zero Magnetic Field ◽  
High Magnetic Fields ◽  
Complex Interplay ◽  
Electron Hole ◽  
Quantum Hall State

Bilayer graphene has a distinctive electronic structure influenced by a complex interplay between various degrees of freedom. We probed its chemical potential using double bilayer graphene heterostructures, separated by a hexagonal boron nitride dielectric. The chemical potential has a nonlinear carrier density dependence and bears signatures of electron-electron interactions. The data allowed a direct measurement of the electric field–induced bandgap at zero magnetic field, the orbital Landau level (LL) energies, and the broken-symmetry quantum Hall state gaps at high magnetic fields. We observe spin-to-valley polarized transitions for all half-filled LLs, as well as emerging phases at filling factors ν = 0 and ν = ±2. Furthermore, the data reveal interaction-driven negative compressibility and electron-hole asymmetry in N = 0, 1 LLs.

scholarly journals Electron-hole asymmetric integer and fractional quantum Hall effect in bilayer graphene

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 55-57 ◽  
Author(s):  
A. Kou ◽  
B. E. Feldman ◽  
A. J. Levin ◽  
B. I. Halperin ◽  
K. Watanabe ◽  
...  
Keyword(s):  
Hall Effect ◽  
Quantum Hall Effect ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Fractional Quantum Hall Effect ◽  
Many Body ◽  
Electron Hole ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Lowest Landau Level

The nature of fractional quantum Hall (FQH) states is determined by the interplay between the Coulomb interaction and the symmetries of the system. The distinct combination of spin, valley, and orbital degeneracies in bilayer graphene is predicted to produce an unusual and tunable sequence of FQH states. Here, we present local electronic compressibility measurements of the FQH effect in the lowest Landau level of bilayer graphene. We observe incompressible FQH states at filling factors ν = 2p + 2/3, with hints of additional states appearing at ν = 2p + 3/5, where p = –2, –1, 0, and 1. This sequence breaks particle-hole symmetry and obeys a ν → ν + 2 symmetry, which highlights the importance of the orbital degeneracy for many-body states in 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.

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