791 research outputs found
Topological Phase Transition in the Quantum Hall Effect
The double layer fractional quantum Hall system is studied using
the edge state formalism and finite-size diagonalization subject to periodic
boundary conditions. Transitions between three different ground states are
observed as the separation as well as the tunneling between the two layers is
varied. Experimental consequences are discussed.Comment: 11 pages, REVTEX v3.0, 7 figure
Degeneracy of Multi-Component Quantum Hall States Satisfying Periodic Boundary Conditions
In systems subject to periodic boundary conditions, Haldane has shown that
states at arbitrary filling fraction possess a degeneracy with respect to
center of mass translations. An analysis is carried out for multi-component
electron systems and extra degeneracies are shown to exist. Their application
to numerical studies is discussed.Comment: 16 pages, REVTEX v3.0, revised manuscrip
Magnetic-Field-Induced Hybridization of Electron Subbands in a Coupled Double Quantum Well
We employ a magnetocapacitance technique to study the spectrum of the soft
two-subband (or double-layer) electron system in a parabolic quantum well with
a narrow tunnel barrier in the centre. In this system unbalanced by gate
depletion, at temperatures T\agt 30 mK we observe two sets of quantum
oscillations: one originates from the upper electron subband in the
closer-to-the-gate part of the well and the other indicates the existence of
common gaps in the spectrum at integer fillings. For the lowest filling factors
and , both the common gap presence down to the point of one- to
two-subband transition and their non-trivial magnetic field dependences point
to magnetic-field-induced hybridization of electron subbands.Comment: Major changes, added one more figure, the latest version to be
published in JETP Let
Half-Integral Spin-Singlet Quantum Hall Effect
We provide numerical evidence that the ground state of a short range
interaction model at is incompressible and spin-singlet for a wide
range of repulsive interactions. Furthermore it is accurately described by a
trial wave function studied earlier. For the Coulomb interaction we find that
this wave function provides a good description of the lowest lying spin-singlet
state, and propose that fractional quantum Hall effect would occur at
if this state became the global ground state.Comment: Latex 13 pages, 3 figures upon reques
Quantum Hall effect in single wide quantum wells
We study the quantum Hall states in the lowest Landau level for a single wide
quantum well. Due to a separation of charges to opposite sides of the well, a
single wide well can be modelled as an effective two level system. We provide
numerical evidence of the existence of a phase transition from an
incompressible to a compressible state as the electron density is increased for
specific well width. Our numerical results show a critical electron density
which depends on well width, beyond which a transition incompressible double
layer quantum Hall state to a mono-layer compressible state occurs. We also
calculate the related phase boundary corresponding to destruction of the
collective mode energy gap. We show that the effective tunneling term and the
interlayer separation are both renormalised by the strong magnetic field. We
also exploite the local density functional techniques in the presence of strong
magnetic field at to calculate renormalized . The
numerical results shows good agreement between many-body calculations and local
density functional techniques in the presence of a strong magnetic field at
. we also discuss implications of this work on the
incompressible state observed in SWQW.Comment: 30 pages, 7 figures (figures are not included
Dynamical Evolution of Boson Stars II: Excited States and Self-Interacting Fields
The dynamical evolution of self-gravitating scalar field configurations in
numerical relativity is studied. The previous analysis on ground state boson
stars of non-interacting fields is extended to excited states and to fields
with self couplings.
Self couplings can significantly change the physical dimensions of boson
stars, making them much more astrophysically interesting (e.g., having mass of
order 0.1 solar mass). The stable () and unstable () branches of
equilibrium configurations of boson stars of self-interacting fields are
studied; their behavior under perturbations and their quasi-normal oscillation
frequencies are determined and compared to the non-interacting case.
Excited states of boson stars with and without self-couplings are studied and
compared. Excited states also have equilibrium configurations with and
branch structures; both branches are intrinsically unstable under a generic
perturbation but have very different instability time scales. We carried out a
detailed study of the instability time scales of these configurations. It is
found that highly excited states spontaneously decay through a cascade of
intermediate states similar to atomic transitions.Comment: 16 pages+ 13 figures . All figures are available at
http://wugrav.wustl.edu/Paper
Notes on the integration of numerical relativity waveforms
A primary goal of numerical relativity is to provide estimates of the wave
strain, , from strong gravitational wave sources, to be used in detector
templates. The simulations, however, typically measure waves in terms of the
Weyl curvature component, . Assuming Bondi gauge, transforming to the
strain reduces to integration of twice in time. Integrations
performed in either the time or frequency domain, however, lead to secular
non-linear drifts in the resulting strain . These non-linear drifts are not
explained by the two unknown integration constants which can at most result in
linear drifts. We identify a number of fundamental difficulties which can arise
from integrating finite length, discretely sampled and noisy data streams.
These issues are an artifact of post-processing data. They are independent of
the characteristics of the original simulation, such as gauge or numerical
method used. We suggest, however, a simple procedure for integrating numerical
waveforms in the frequency domain, which is effective at strongly reducing
spurious secular non-linear drifts in the resulting strain.Comment: 23 pages, 10 figures, matches final published versio
Fermionic Chern-Simons theory for the Fractional Quantum Hall Effect in Bilayers
We generalize the fermion Chern-Simons theory for the Fractional Hall Effect
(FQHE) which we developed before, to the case of bilayer systems. We study the
complete dynamic response of these systems and predict the experimentally
accessible optical properties. In general, for the so called
states, we find that the spectrum of collective excitations has a gap, and the
wave function has the Jastrow-Slater form, with the exponents determined by the
coefficients , and . We also find that the states, {\it
i.~e.~}, those states whose filling fraction is , have a gapless mode
which may be related with the spontaneous appearance of the interlayer
coherence. Our results also indicate that the gapless mode makes a contribution
to the wave function of the states analogous to the phonon
contribution to the wave function of superfluid . We calculate the
Hall conductance, and the charge and statistics of the quasiparticles. We also
present an generalization of this theory relevant to spin unpolarized
or partially polarized single layers.Comment: 55 pages, Urbana Prepin
Computational Relativistic Astrophysics With Adaptive Mesh Refinement: Testbeds
We have carried out numerical simulations of strongly gravitating systems
based on the Einstein equations coupled to the relativistic hydrodynamic
equations using adaptive mesh refinement (AMR) techniques. We show AMR
simulations of NS binary inspiral and coalescence carried out on a workstation
having an accuracy equivalent to that of a regular unigrid simulation,
which is, to the best of our knowledge, larger than all previous simulations of
similar NS systems on supercomputers. We believe the capability opens new
possibilities in general relativistic simulations.Comment: 7 pages, 16 figure
Towards a Singularity-Proof Scheme in Numerical Relativity
Progress in numerical relativity has been hindered for 30 years because of
the difficulties of avoiding spacetime singularities in numerical evolution. We
propose a scheme which excises a region inside an apparent horizon containing
the singularity. Two major ingredients of the scheme are the use of a
horizon-locking coordinate and a finite differencing which respects the causal
structure of the spacetime. Encouraging results of the scheme in the spherical
collapse case are given.Comment: 9 page
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