1,492 research outputs found
Nonlinear Transport in a Quantum Point Contact due to Soft Disorder Induced Coherent Mode Mixing
We show that the coherent mixing of different transverse modes, due to
forward scattering of carriers by soft impurity- or boundary potentials leads
to a nonlinear, asymmetric current response of quantum point contacts (QPC).
The oscillating contribution to the current is sensitive both to driving
voltage and to gate voltage in direct analogy to the electrostatic
Aharonov-Bohm effect.
Our calculations are in a good agreement with recent experimental data
showing small-scale conductivity nonlinearities and asymmetry in QPC.Comment: 4 pages, 2 figures (availiable upon request), REVTEX, Applied Physics
Report 93-4
Quantum fluctuations of classical skyrmions in quantum Hall Ferromagnets
In this article, we discuss the effect of the zero point quantum fluctuations
to improve the results of the minimal field theory which has been applied to
study %SMG the skyrmions in the quantum Hall systems. Our calculation which is
based on the semiclassical treatment of the quantum fluctuations, shows that
the one-loop quantum correction provides more accurate results for the minimal
field theory.Comment: A few errors are corrected. Accepted for publication in Rapid
Communication, Phys. Rev.
Distribution of Wigner delay time from single channel disordered systems
We consider the scattering of an electron from a semi-infinite
one-dimensional random medium. The random medium is characterized by force,
-\d V/\d L being the basic random variable. We obtain an analytical
expression for the stationary delay time () distribution
within a random phase approximation. Our result agrees with earlier analytical
expressions, where the random potential is taken to be of different kind,
indicating universality of the delay time distribution, i.e., delay time
distribution is independent of the nature of disorder.Comment: 8 pages RevTeX, no figure
Dynamics of the Compact, Ferromagnetic \nu=1 Edge
We consider the edge dynamics of a compact, fully spin polarized state at
filling factor . We show that there are two sets of collective
excitations localized near the edge: the much studied, gapless, edge
magnetoplasmon but also an additional edge spin wave that splits off below the
bulk spin wave continuum. We show that both of these excitations can soften at
finite wave-vectors as the potential confining the system is softened, thereby
leading to edge reconstruction by spin texture or charge density wave
formation. We note that a commonly employed model of the edge confining
potential is non-generic in that it systematically underestimates the texturing
instability.Comment: 13 pages, 7 figures, Revte
Statistical properties of phases and delay times of the one-dimensional Anderson model with one open channel
We study the distribution of phases and of Wigner delay times for a
one-dimensional Anderson model with one open channel. Our approach, based on
classical Hamiltonian maps, allows us an analytical treatment. We find that the
distribution of phases depends drastically on the parameter where is the variance of the disorder distribution and
the wavevector. It undergoes a transition from uniformity to singular
behaviour as increases. The distribution of delay times shows
universal power law tails , while the short time behaviour is
- dependent.Comment: 4 pages, 2 figures, Submitted to PR
Magnetic fields in cosmic particle acceleration sources
We review here some magnetic phenomena in astrophysical particle accelerators
associated with collisionless shocks in supernova remnants, radio galaxies and
clusters of galaxies. A specific feature is that the accelerated particles can
play an important role in magnetic field evolution in the objects. We discuss a
number of CR-driven, magnetic field amplification processes that are likely to
operate when diffusive shock acceleration (DSA) becomes efficient and
nonlinear. The turbulent magnetic fields produced by these processes determine
the maximum energies of accelerated particles and result in specific features
in the observed photon radiation of the sources. Equally important, magnetic
field amplification by the CR currents and pressure anisotropies may affect the
shocked gas temperatures and compression, both in the shock precursor and in
the downstream flow, if the shock is an efficient CR accelerator. Strong
fluctuations of the magnetic field on scales above the radiation formation
length in the shock vicinity result in intermittent structures observable in
synchrotron emission images. Resonant and non-resonant CR streaming
instabilities in the shock precursor can generate mesoscale magnetic fields
with scale-sizes comparable to supernova remnants and even superbubbles. This
opens the possibility that magnetic fields in the earliest galaxies were
produced by the first generation Population III supernova remnants and by
clustered supernovae in star forming regions.Comment: 30 pages, Space Science Review
Abelian Magnetic Monopole Dominance in Quark Confinement
We prove Abelian magnetic monopole dominance in the string tension of QCD.
Abelian and monopole dominance in low energy physics of QCD has been confirmed
for various quantities by recent Monte Carlo simulations of lattice gauge
theory. In order to prove this dominance, we use the reformulation of continuum
Yang-Mills theory in the maximal Abelian gauge as a deformation of a
topological field theory of magnetic monopoles, which was proposed in the
previous article by the author. This reformulation provides an efficient way
for incorporating the magnetic monopole configuration as a topological
non-trivial configuration in the functional integral. We derive a version of
the non-Abelian Stokes theorem and use it to estimate the expectation value of
the Wilson loop. This clearly exhibits the role played by the magnetic monopole
as an origin of the Berry phase in the calculation of the Wilson loop in the
manifestly gauge invariant manner. We show that the string tension derived from
the diagonal (abelian) Wilson loop in the topological field theory (studied in
the previous article) converges to that of the full non-Abelian Wilson loop in
the limit of large Wilson loop. Therefore, within the above reformulation of
QCD, this result (together with the previous result) completes the proof of
quark confinement in QCD based on the criterion of the area law of the full
non-Abelian Wilson loop.Comment: 33 pages, Latex, no figures, version accepted for publication in
Phys. Rev. D (additions of sec. 4.5 and references, and minor changes
Universal Correlations of Coulomb Blockade Conductance Peaks and the Rotation Scaling in Quantum Dots
We show that the parametric correlations of the conductance peak amplitudes
of a chaotic or weakly disordered quantum dot in the Coulomb blockade regime
become universal upon an appropriate scaling of the parameter. We compute the
universal forms of this correlator for both cases of conserved and broken time
reversal symmetry. For a symmetric dot the correlator is independent of the
details in each lead such as the number of channels and their correlation. We
derive a new scaling, which we call the rotation scaling, that can be computed
directly from the dot's eigenfunction rotation rate or alternatively from the
conductance peak heights, and therefore does not require knowledge of the
spectrum of the dot. The relation of the rotation scaling to the level velocity
scaling is discussed. The exact analytic form of the conductance peak
correlator is derived at short distances. We also calculate the universal
distributions of the average level width velocity for various values of the
scaled parameter. The universality is illustrated in an Anderson model of a
disordered dot.Comment: 35 pages, RevTex, 6 Postscript figure
Aspects of Magnetic Field Configurations in Planar Nonlinear Electrodynamics
In the framework of three-dimensional Born-Infeld Electrodynamics, we pursue
an investigation of the consequences of the space-time dimensionality on the
existence of magnetostatic fields generated by electric charges at rest in an
inertial frame, which are present in its four-dimensional version. Our analysis
reveals interesting features of the model. In fact, a magnetostatic field
associated with an electric charge at rest does not appear in this case.
Interestingly, the addition of the topological term (Chern-Simons) to
Born-Infeld Electrodynamics yields the appearance of the magnetostatic field.
We also contemplate the fields associated to the would-be-magnetic monopole in
three dimensions.Comment: 8 page
Comparison of Radiation Damage in Lead Tungstate Crystals under Pion and Gamma Irradiation
Studies of the radiation hardness of lead tungstate crystals produced by the
Bogoroditsk Techno-Chemical Plant in Russia and the Shanghai Institute of
Ceramics in China have been carried out at IHEP, Protvino. The crystals were
irradiated by a 40-GeV pion beam. After full recovery, the same crystals were
irradiated using a -ray source. The dose rate profiles along
the crystal length were observed to be quite similar. We compare the effects of
the two types of radiation on the crystals light output.Comment: 10 pages, 8 figures, Latex 2e, 28.04.04 - minor grammatical change
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