12 research outputs found
Intra-Landau level magnetoexcitons and the transition between quantum Hall states in undoped bilayer graphene
We study the collective modes of the quantum Hall states in undoped bilayer
graphene in a strong perpendicular magnetic and electric field. Both for the
well-known ferromagnetic state that is relevant for small electric field
and the analogous valley/layer polarized one suitable for large
, the low energy physics is dominated by magnetoexcitons with zero
angular momentum that are even combinations of excitons that conserve Landau
orbitals. We identify a long wave length instability in both states, and argue
that there is an intermediate range of the electric field where a gapless phase interpolates between the
incompressible quantum Hall states. The experimental relevance of this
crossover via a gapless state is discussed.Comment: 7 pages, 5 figure
Charge-density-wave states in double-layer graphene structures in a high magnetic field
We study the phases of correlated charge-density waves that form at a high
magnetic field in two parallel graphene flakes separated by a thin insulator.
The predicted phases include the square and hexagonal charge-density-wave
bubbles, and a quasi-one-dimensional stripe phase. We find that the transition
temperature for such phases is within the experimentally accessible range and
that formation of interlayer-correlated states produces a negative
compressibility contribution to the differential capacitance of this system.Comment: 6+3 pages, 7 figure
Fractional quantum Hall effect arising from repulsive three body interaction
We consider a collection of fermions in a strong magnetic field coupled by a
purely three body repulsive interaction, and predict the formation of composite
fermions, leading to a remarkably rich phase diagram containing a host of
fractional quantum Hall states, a composite fermion Fermi sea, and a pairing
transition. This is entirely unexpected, because the appearance of composite
fermions and fractional quantum Hall effect is ordinarily thought to be a
result of strong two-body repulsion. Recent theoretical and experimental
breakthroughs in ultra-cold atoms and molecules have facilitated the
realization of such a system, where this physics can be tested.Comment: 4 pages, 4 figure
Nature of excitations of the 5/2 fractional quantum Hall effect
It is shown, with the help of exact diagonalization studies on systems with
up to sixteen electrons, in the presence of up to two delta function
impurities, that the Pfaffian model is inadequate for the actual quasiholes and
quasiparticles of the 5/2 fractional quantum Hall effect. Implications for
non-Abelian statistics are discussed.Comment: 4 pages, 2 figure