9,556 research outputs found
Phase Diagram for Quantum Hall Bilayers at
We present a phase diagram for a double quantum well bilayer electron gas in
the quantum Hall regime at total filling factor , based on exact
numerical calculations of the topological Chern number matrix and the
(inter-layer) superfluid density. We find three phases: a quantized Hall state
with pseudo-spin superfluidity, a quantized Hall state with pseudo-spin
``gauge-glass'' order, and a decoupled composite Fermi liquid. Comparison with
experiments provides a consistent explanation of the observed quantum Hall
plateau, Hall drag plateau and vanishing Hall drag resistance, as well as the
zero-bias conductance peak effect, and suggests some interesting points to
pursue experimentally.Comment: 4 pages with 4 figure
Broken-Symmetry States of Dirac Fermions in Graphene with A Partially Filled High Landau Level
We report on numerical study of the Dirac fermions in partially filled N=3
Landau level (LL) in graphene. At half-filling, the equal-time density-density
correlation function displays sharp peaks at nonzero wavevectors . Finite-size scaling shows that the peak value grows with electron
number and diverges in the thermodynamic limit, which suggests an instability
toward a charge density wave. A symmetry broken stripe phase is formed at large
system size limit, which is robust against purturbation from disorder
scattering. Such a quantum phase is experimentally observable through transport
measurements. Associated with the special wavefunctions of the Dirac LL, both
stripe and bubble phases become possible candidates for the ground state of the
Dirac fermions in graphene with lower filling factors in the N=3 LL.Comment: Contains are slightly changed. Journal reference and DOI are adde
Odd-Integer Quantum Hall Effect in Graphene: Interaction and Disorder Effects
We study the competition between the long-range Coulomb interaction, disorder
scattering, and lattice effects in the integer quantum Hall effect (IQHE) in
graphene. By direct transport calculations, both and IQHE
states are revealed in the lowest two Dirac Landau levels. However, the
critical disorder strength above which the IQHE is destroyed is much
smaller than that for the IQHE, which may explain the absence of a
plateau in recent experiments. While the excitation spectrum in the
IQHE phase is gapless within numerical finite-size analysis, we do find and
determine a mobility gap, which characterizes the energy scale of the stability
of the IQHE. Furthermore, we demonstrate that the IQHE state is a Dirac
valley and sublattice polarized Ising pseudospin ferromagnet, while the
state is an plane polarized pseudospin ferromagnet.Comment: 5 pages, 5 figure
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