34,601 research outputs found
Tunnel transport and interlayer excitons in bilayer fractional quantum Hall systems
In a bilayer system consisting of a composite-fermion Fermi sea in each
layer, the tunnel current is exponentially suppressed at zero bias, followed by
a strong peak at a finite bias voltage . This behavior, which is
qualitatively different from that observed for the electron Fermi sea, provides
fundamental insight into the strongly correlated non-Fermi liquid nature of the
CF Fermi sea and, in particular, offers a window into the short-distance
high-energy physics of this state. We identify the exciton responsible for the
peak current and provide a quantitative account of the value of .
The excitonic attraction is shown to be quantitatively significant, and its
variation accounts for the increase of with the application of an
in-plane magnetic field. We also estimate the critical Zeeman energy where
transition occurs from a fully spin polarized composite fermion Fermi sea to a
partially spin polarized one, carefully incorporating corrections due to finite
width and Landau level mixing, and find it to be in satisfactory agreement with
the Zeeman energy where a qualitative change has been observed for the onset
bias voltage [Eisenstein et al., Phys. Rev. B 94, 125409 (2016)]. For
fractional quantum Hall states, we predict a substantial discontinuous jump in
when the system undergoes a transition from a fully spin
polarized state to a spin singlet or a partially spin polarized state.Comment: 14 pages, 14 figure
A flat space-time model of the Universe
We propose a model of the Universe based on Minkowski flat space-time metric.
In this model the space-time does not evolve. Instead the matter evolves such
that all the mass parameters increase with time. We construct a model based on
unimodular gravity to show how this can be accomplished within the framework of
flat space-time. We show that the model predicts the Hubble law if the masses
increase with time. Furthermore we show that it fits the high z supernova data
in a manner almost identical to the standard Big Bang model. Furthermore we
show that at early times the Universe is dominated by radiative energy density.
The phenomenon of recombination also arises in our model and hence predicts the
existence of CMBR. However a major difference with the standard Big Bang is
that the radiative temperature and energy density does not evolve in our model.
Furthermore we argue that the basic motivation for inflation is absent in our
model.Comment: 11 pages, no figures, changes in presentatio
The Virgo Alignment Puzzle in Propagation of Radiation on Cosmological Scales
We reconsider analysis of data on the cosmic microwave background on the
largest angular scales. Temperature multipoles of any order factor naturally
into a direct product of axial quantities and cosets. Striking coincidences
exist among the axes associated with the dipole, quadrupole, and octupole CMB
moments. These axes also coincide well with two other axes independently
determined from polarizations at radio and optical frequencies propagating on
cosmological scales. The five coincident axes indicate physical correlation and
anisotropic properties of the cosmic medium not predicted by the conventional
Big Bang scenario. We consider various mechanisms, including foreground
corrections, as candidates for the observed correlations. We also consider
whether the propagation anomalies may be a signal of ``dark energy'' in the
form of a condensed background field. Perhaps {\it light propagation} will
prove to be an effective way to look for the effects of {\it dark energy}.Comment: 24 pages, 4 figures, minor changes, no change in result or
conclusions. to appear in IJMP
Covariant Symmetry Classifications for Observables of Cosmological Birefringence
Polarizations of electromagnetic waves from distant galaxies are known to be
correlated with the source orientations. These quantities have been used to
search for signals of cosmological birefringence. We review and classify
transformation properties of the polarization and source orientation
observables. The classifications give a firm foundation to certain practices
which have sprung up informally in the literature. Transformations under parity
play a central role, showing that parity violation in emission or in the
subsequent propagation is an observable phenomenon. We also discuss statistical
measures, correlations and distributions which transform properly and which can
be used for systematic data analysis.Comment: 8 pages, revtex, 1 postscript figur
Nonuniversal exponents in sandpiles with stochastic particle number transfer
We study fixed density sandpiles in which the number of particles transferred
to a neighbor on relaxing an active site is determined stochastically by a
parameter . Using an argument, the critical density at which an
active-absorbing transition occurs is found exactly. We study the critical
behavior numerically and find that the exponents associated with both static
and time-dependent quantities vary continuously with .Comment: Some parts rewritten, results unchanged. To appear in Europhys. Let
Activation gaps for the fractional quantum Hall effect: realistic treatment of transverse thickness
The activation gaps for fractional quantum Hall states at filling fractions
are computed for heterojunction, square quantum well, as well as
parabolic quantum well geometries, using an interaction potential calculated
from a self-consistent electronic structure calculation in the local density
approximation. The finite thickness is estimated to make 30% correction
to the gap in the heterojunction geometry for typical parameters, which
accounts for roughly half of the discrepancy between the experiment and
theoretical gaps computed for a pure two dimensional system. Certain model
interactions are also considered. It is found that the activation energies
behave qualitatively differently depending on whether the interaction is of
longer or shorter range than the Coulomb interaction; there are indications
that fractional Hall states close to the Fermi sea are destabilized for the
latter.Comment: 32 pages, 13 figure
Optimisation of a Brownian dynamics algorithm for semidilute polymer solutions
Simulating the static and dynamic properties of semidilute polymer solutions
with Brownian dynamics (BD) requires the computation of a large system of
polymer chains coupled to one another through excluded-volume and hydrodynamic
interactions. In the presence of periodic boundary conditions, long-ranged
hydrodynamic interactions are frequently summed with the Ewald summation
technique. By performing detailed simulations that shed light on the influence
of several tuning parameters involved both in the Ewald summation method, and
in the efficient treatment of Brownian forces, we develop a BD algorithm in
which the computational cost scales as O(N^{1.8}), where N is the number of
monomers in the simulation box. We show that Beenakker's original
implementation of the Ewald sum, which is only valid for systems without bead
overlap, can be modified so that \theta-solutions can be simulated by switching
off excluded-volume interactions. A comparison of the predictions of the radius
of gyration, the end-to-end vector, and the self-diffusion coefficient by BD,
at a range of concentrations, with the hybrid Lattice Boltzmann/Molecular
Dynamics (LB/MD) method shows excellent agreement between the two methods. In
contrast to the situation for dilute solutions, the LB/MD method is shown to be
significantly more computationally efficient than the current implementation of
BD for simulating semidilute solutions. We argue however that further
optimisations should be possible.Comment: 17 pages, 8 figures, revised version to appear in Physical Review E
(2012
Logarithmic temperature dependence of conductivity at half-integer filling factors: Evidence for interaction between composite fermions
We have studied the temperature dependence of diagonal conductivity in
high-mobility two-dimensional samples at filling factors and 3/2 at
low temperatures. We observe a logarithmic dependence on temperature, from our
lowest temperature of 13 mK up to 400 mK. We attribute the logarithmic
correction to the effects of interaction between composite fermions, analogous
to the Altshuler-Aronov type correction for electrons at zero magnetic field.
The paper is accepted for publication in Physical Review B, Rapid
Communications.Comment: uses revtex macro
Composite fermion wave functions as conformal field theory correlators
It is known that a subset of fractional quantum Hall wave functions has been
expressed as conformal field theory (CFT) correlators, notably the Laughlin
wave function at filling factor ( odd) and its quasiholes, and the
Pfaffian wave function at and its quasiholes. We develop a general
scheme for constructing composite-fermion (CF) wave functions from conformal
field theory. Quasiparticles at are created by inserting anyonic
vertex operators, , that replace a subset of the electron
operators in the correlator. The one-quasiparticle wave function is identical
to the corresponding CF wave function, and the two-quasiparticle wave function
has correct fractional charge and statistics and is numerically almost
identical to the corresponding CF wave function. We further show how to exactly
represent the CF wavefunctions in the Jain series as the CFT
correlators of a new type of fermionic vertex operators, ,
constructed from free compactified bosons; these operators provide the CFT
representation of composite fermions carrying flux quanta in the CF Landau level. We also construct the corresponding quasiparticle- and
quasihole operators and argue that they have the expected fractional charge and
statistics. For filling fractions 2/5 and 3/7 we show that the chiral CFTs that
describe the bulk wave functions are identical to those given by Wen's general
classification of quantum Hall states in terms of -matrices and - and
-vectors, and we propose that to be generally true. Our results suggest a
general procedure for constructing quasiparticle wave functions for other
fractional Hall states, as well as for constructing ground states at filling
fractions not contained in the principal Jain series.Comment: 26 pages, 3 figure
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