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 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 Beyond anyons

2018 ◽  
Vol 33 (28) ◽  
pp. 1830011
Author(s):  
Zhenghan Wang
Keyword(s):  
Black Holes ◽  
Quantum Gravity ◽  
Quantum Hall ◽  
Group Symmetry ◽  
Topological Order ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Btz Black Holes ◽  
Modular Tensor Categories ◽  
Interesting Direction

The theory of anyon systems, as modular functors topologically and unitary modular tensor categories algebraically, is mature. To go beyond anyons, our first step is the interplay of anyons with conventional group symmetry due to the paramount importance of group symmetry in physics. This led to the theory of symmetry-enriched topological order. Another direction is the boundary physics of topological phases, both gapless as in the fractional quantum Hall physics and gapped as in the toric code. A more speculative and interesting direction is the study of Banados–Teitelboim–Zanelli (BTZ) black holes and quantum gravity in 3d. The clearly defined physical and mathematical issues require a far-reaching generalization of anyons and seem to be within reach. In this short survey, I will first cover the extensions of anyon theory to symmetry defects and gapped boundaries. Then, I will discuss a desired generalization of anyons to anyon-like objects — the BTZ black holes — in 3d quantum gravity.

Fractional Quantum Hall States in Bilayer Graphene Probed by Transconductance Fluctuations

Nano Letters ◽  
2015 ◽  
Vol 15 (11) ◽  
pp. 7445-7451 ◽  
Author(s):  
Youngwook Kim ◽  
Dong Su Lee ◽  
Suyong Jung ◽  
Viera Skákalová ◽  
T. Taniguchi ◽  
...  
Keyword(s):  
Quantum Hall ◽  
Bilayer Graphene ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Quantum Hall States ◽  
Hall States

scholarly journals Gap Reversal at Filling Factors3+1/3and3+1/5: Towards Novel Topological Order in the Fractional Quantum Hall Regime

2015 ◽  
Vol 114 (7) ◽  
Author(s):  
Ethan Kleinbaum ◽  
Ashwani Kumar ◽  
L. N. Pfeiffer ◽  
K. W. West ◽  
G. A. Csáthy
Keyword(s):  
Quantum Hall ◽  
Topological Order ◽  
Fractional Quantum ◽  
Fractional Quantum Hall ◽  
Quantum Hall Regime ◽  
Hall Regime

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 Robust fractional quantum Hall effect in the N=2 Landau level in bilayer graphene

2016 ◽  
Vol 7 (1) ◽  
Author(s):  
Georgi Diankov ◽  
Chi-Te Liang ◽  
François Amet ◽  
Patrick Gallagher ◽  
Menyoung Lee ◽  
...  
Keyword(s):  
Hall Effect ◽  
Landau Level ◽  
Quantum Hall Effect ◽  
Quantum Hall ◽  
Bilayer Graphene ◽  
Fractional Quantum Hall Effect ◽  
Fractional Quantum ◽  
Fractional Quantum Hall
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