Biased bilayer graphene as a helical quantum Hall ferromagnet

Côté, R.; Fouquet, Jérémie P.; Luo, Wei

doi:10.1103/physrevb.84.235301

Cited by 20 publications

(31 citation statements)

References 36 publications

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“…This orbital degeneracy brings about a new realm of quantum phenomena, [13][14][15][16][17][18] such as orbital mixing and orbital-pseudospin waves. The eightfold degeneracy of the zero-energy levels is partially or fully lifted in the presence of Zeeman coupling, interlayer bias and Coulomb interactions, and these levels evolve into a variety of pseudo-zero-mode levels, or brokensymmetry states, as discussed theoretically in the context of quantum-Hall ferromagnetism 13 and others.…”

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confidence: 99%

Structure and the Lamb-shift-like quantum splitting of the pseudo-zero-mode Landau levels in bilayer graphene

Shizuya

2012

Phys. Rev. B

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In a magnetic field bilayer graphene supports an octet of zero-energy Landau levels with an extra twofold degeneracy in Landau orbitals n = 0 and n = 1. It is shown that this orbital degeneracy is lifted due to Coulombic quantum fluctuations of the valence band (the Dirac sea); this is a quantum effect analogous to the Lamb shift in the hydrogen atom. A detailed study is made of how these zero-energy levels evolve, with filling, into a variety of pseudo-zero-mode Landau levels in the presence of possible spin and valley breaking and Coulomb interactions, and a comparison is made with experimental results.

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Structure and the Lamb-shift-like quantum splitting of the pseudo-zero-mode Landau levels in bilayer graphene

Shizuya

2012

Phys. Rev. B

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“…The summation allows the capture of modes that originate from a folding of the full dispersion into the first Brillouin zone. It also captures the electron-hole continuum 30 that starts at the Hartree-Fock gap. In Fig.…”

Section: This Equation Ismentioning

confidence: 99%

Charge density wave with meronlike spin texture induced by a lateral superlattice in a two-dimensional electron gas

Côté

Bazier-Matte

2016

Phys. Rev. B

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The combined effect of a lateral square superlattice potential and the Coulomb interaction on the ground state of a two-dimensional electron gas in a perpendicular magnetic field is studied for different rational values of Γ, the inverse of the number of flux quanta per unit cell of the external potential, at filling factor ν = 1 in Landau level N = 0. When Landau level mixing and disorder effects are neglected, increasing the strength W0 of the potential induces a transition, at a critical strength W (c) 0 , from a uniform and fully spin polarized state to a two-dimensional charge density wave (CDW) with a meronlike spin texture at each maximum and minimum of the CDW. The collective excitations of this "vortex-CDW" are similar to those of the Skyrme crystal that is expected to be the ground state near filling factor ν = 1. In particular, a broken U(1) symmetry in the vortex-CDW results in an extra gapless phase mode that could provide a fast channel for the relaxation of nuclear spins. The average spin polarization Sz changes in a continuous or discontinuous manner as W0 is increased depending on whether Γ ∈ [1/2, 1] or Γ ∈ [0, 1/2] . The phase mode and the meronlike spin texture disappear at large value of W0, leaving as the ground state partially spin-polarized CDW if Γ = 1/2 or a spin-unpolarized CDW if Γ = 1/2.

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“…But, at special filling factors ν = 1, 3, a sequence of phase transitions involving uniform and nonuniform states is also possible. 3,8,9 The nonuniform states occur in a region of bias where the system can be described as an orbital QHF i.e. where the electrons collectively condense into a linear combination of the n = 0 and n = 1 orbitals.…”

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confidence: 99%

Electromagnetic absorption and Kerr effect in quantum Hall ferromagnetic states of bilayer graphene

2015

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In a quantizing magnetic field, the chiral two-dimensional electron gas in Landau level N = 0 of bilayer graphene goes through a series of phase transitions at integer filling factors ν ∈ [−3, 3] when the strength of an electric field applied perpendicularly to the layers is increased. At filling factor ν = 3, the electron gas can described by a simple two-level system where layer and spin degrees of freedom are frozen. The gas then behaves as an orbital quantum Hall ferromagnet. A Coulomb-induced Dzyaloshinskii-Moriya term in the orbital pseudospin Hamiltonian is responsible for a series of transitions first to a Wigner crystal state and then to a spiral state as the electric field is increased. Both states have a non trivial orbital pseudospin texture. In this work, we study how the phase diagram at ν = 3 is modified by an electric field applied in the plane of the layers and then derive several experimental signatures of the uniform and nonuniform states in the phase diagram. In addition to the transport gap, we study the electromagnetic absorption and the Kerr rotation due to the excitations of the orbital pseudospin-wave modes in the broken-symmetry states.

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Biased bilayer graphene as a helical quantum Hall ferromagnet

Cited by 20 publications

References 36 publications

Structure and the Lamb-shift-like quantum splitting of the pseudo-zero-mode Landau levels in bilayer graphene

Structure and the Lamb-shift-like quantum splitting of the pseudo-zero-mode Landau levels in bilayer graphene

Charge density wave with meronlike spin texture induced by a lateral superlattice in a two-dimensional electron gas

Electromagnetic absorption and Kerr effect in quantum Hall ferromagnetic states of bilayer graphene

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