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 Spin-valley coherent phases of the ν=0 quantum Hall state in bilayer graphene

2017 ◽  
Vol 96 (24) ◽  
Author(s):  
Ganpathy Murthy ◽  
Efrat Shimshoni ◽  
H. A. Fertig
Keyword(s):  
Quantum Hall ◽  
Bilayer Graphene ◽  
Quantum Hall State

scholarly journals Tunable fractional quantum Hall phases in bilayer graphene

Science ◽  
2014 ◽  
Vol 345 (6192) ◽  
pp. 61-64 ◽  
Author(s):  
Patrick Maher ◽  
Lei Wang ◽  
Yuanda Gao ◽  
Carlos Forsythe ◽  
Takashi Taniguchi ◽  
...  
Keyword(s):  
Symmetry Breaking ◽  
Electric Field ◽  
Degrees Of Freedom ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Emergent Behavior ◽  
Topological Order ◽  
Fractional Quantum Hall ◽  
Model Platform ◽  
Quantizing Magnetic Field

Symmetry-breaking in a quantum system often leads to complex emergent behavior. In bilayer graphene (BLG), an electric field applied perpendicular to the basal plane breaks the inversion symmetry of the lattice, opening a band gap at the charge neutrality point. In a quantizing magnetic field, electron interactions can cause spontaneous symmetry-breaking within the spin and valley degrees of freedom, resulting in quantum Hall effect (QHE) states with complex order. Here, we report fractional QHE states in BLG that show phase transitions that can be tuned by a transverse electric field. This result provides a model platform with which to study the role of symmetry-breaking in emergent states with topological order.

scholarly journals Explanation of ν = −½ fractional quantum Hall state in bilayer graphene

2016 ◽  
Vol 472 (2186) ◽  
pp. 20150330 ◽  
Author(s):  
J. Jacak ◽  
L. Jacak
Keyword(s):  
Experimental Data ◽  
Quantum Hall Effect ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Fractional Quantum Hall Effect ◽  
Landau Levels ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Quantum Hall State ◽  
Good Agreement

The commensurability condition is applied to determine the hierarchy of fractional filling of Landau levels for fractional quantum Hall effect (FQHE) in monolayer and bilayer graphene. Good agreement with experimental data is achieved. The presence of even-denominator filling fractions in the hierarchy of the FQHE in bilayer graphene is explained, including the state at ν = − 1 2 .

scholarly journals Metallic Phase and Temperature Dependence of the ν=0 Quantum Hall State in Bilayer Graphene

2019 ◽  
Vol 122 (9) ◽  
Author(s):  
Jing Li ◽  
Hailong Fu ◽  
Zhenxi Yin ◽  
Kenji Watanabe ◽  
Takashi Taniguchi ◽  
...  
Keyword(s):  
Temperature Dependence ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Metallic Phase ◽  
Quantum Hall State

scholarly journals Isospin magnetism and spin-polarized superconductivity in Bernal bilayer graphene

Science ◽  
2022 ◽  
Author(s):  
Haoxin Zhou ◽  
Ludwig Holleis ◽  
Yu Saito ◽  
Liam Cohen ◽  
William Huynh ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Order Parameter ◽  
Degrees Of Freedom ◽  
Bilayer Graphene ◽  
Zero Magnetic Field ◽  
Cooper Pairing ◽  
Two Dimensional ◽  
Van Hove Singularity ◽  
Spin Polarized ◽  
Spin Triplet

In conventional superconductors, Cooper pairing occurs between electrons of opposite spin. We observe spin-polarized superconductivity in Bernal bilayer graphene when doped to a saddle-point van Hove singularity generated by large applied perpendicular electric field. We observe a cascade of electrostatic gate-tuned transitions between electronic phases distinguished by their polarization within the isospin space defined by the combination of the spin and momentum-space valley degrees of freedom. Although all of these phases are metallic at zero magnetic field, we observe a transition to a superconducting state at finite B ‖ ≈ 150mT applied parallel to the two-dimensional sheet. Superconductivity occurs near a symmetry breaking transition, and exists exclusively above the B ‖ -limit expected of a paramagnetic superconductor with the observed transition temperature T C ≈ 30mK, consistent with a spin-triplet order parameter.

scholarly journals Composite particle construction of the Fibonacci fractional quantum Hall state

2021 ◽  
Vol 103 (23) ◽  
Author(s):  
Hart Goldman ◽  
Ramanjit Sohal ◽  
Eduardo Fradkin
Keyword(s):  
Composite Particle ◽  
Quantum Hall ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Quantum Hall State
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