528 research outputs found
Interaction-Induced Magnetization of the Two-Dimensional Electron Gas
We consider the contribution of electron-electron interactions to the orbital
magnetization of a two-dimensional electron gas, focusing on the ballistic
limit in the regime of negligible Landau-level spacing. This regime can be
described by combining diagrammatic perturbation theory with semiclassical
techniques. At sufficiently low temperatures, the interaction-induced
magnetization overwhelms the Landau and Pauli contributions. Curiously, the
interaction-induced magnetization is third-order in the (renormalized) Coulomb
interaction. We give a simple interpretation of this effect in terms of
classical paths using a renormalization argument: a polygon must have at least
three sides in order to enclose area. To leading order in the renormalized
interaction, the renormalization argument gives exactly the same result as the
full treatment.Comment: 11 pages including 4 ps figures; uses revtex and epsf.st
Onset of Vortices in Thin Superconducting Strips and Wires
Spontaneous nucleation and the consequent penetration of vortices into thin
superconducting films and wires, subjected to a magnetic field, can be
considered as a nonlinear stage of primary instability of the current-carrying
superconducting state. The development of the instability leads to the
formation of a chain of vortices in strips and helicoidal vortex lines in
wires. The boundary of instability was obtained analytically. The nonlinear
stage was investigated by simulations of the time-dependent generalized
Ginzburg-Landau equation.Comment: REVTeX 3.0, 12 pages, 5Postscript figures (uuencoded). Accepted for
Phys. Rev.
Atom loss and the formation of a molecular Bose-Einstein condensate by Feshbach resonance
In experiments conducted recently at MIT on Na Bose-Einstein condensates [S.
Inouye et al, Nature 392, 151 (1998); J. Stenger et al, Phys. Rev. Lett. 82,
2422 (1999)], large loss rates were observed when a time-varying magnetic field
was used to tune a molecular Feshbach resonance state near the state of a pair
of atoms in the condensate. A collisional deactivation mechanism affecting a
temporarily formed molecular condensate [see V. A. Yurovsky, A. Ben-Reuven, P.
S. Julienne and C. J. Williams, Phys. Rev. A 60, R765 (1999)], studied here in
more detail, accounts for the results of the slow-sweep experiments. A best fit
to the MIT data yields a rate coefficient for deactivating atom-molecule
collisions of 1.6e-10 cm**3/s. In the case of the fast sweep experiment, a
study is carried out of the combined effect of two competing mechanisms, the
three-atom (atom-molecule) or four-atom (molecule-molecule) collisional
deactivation vs. a process of two-atom trap-state excitation by curve crossing
[F. H. Mies, P. S. Julienne, and E. Tiesinga, Phys. Rev. A 61, 022721 (2000)].
It is shown that both mechanisms contribute to the loss comparably and
nonadditively.Comment: LaTeX, 14 pages, 12 PostScript figures, uses REVTeX and psfig,
submitted to Physical Review
Massive triplet excitations in a magnetized anisotropic Haldane spin chain
Inelastic neutron scattering experiments on the Haldane-gap quantum
antiferromagnet \nd are performed at mK temperatures in magnetic fields of
almost twice the critical field applied perpendicular to the spin cahins.
Above a re-opening of the spin gap is clearly observed. In the high-field
N\'eel-ordered state the spectrum is dominated by three distinct long-lived
excitation branches. Several field-theoretical models are tested in a
quantitative comparison with the experimental data.Comment: 4 pages, 3 figure
Dynamics of an anisotropic Haldane antiferromagnet in strong magnetic field
We report the results of elastic and inelastic neutron scattering experiments
on the Haldane gap quantum antiferromagnet Ni(C5D14N2)2N3(PF6) performed at mK
temperatures in a wide range of magnetic field applied parallel to the S = 1
spin chains. Even though this geometry is closest to an ideal axially symmetric
configuration, the Haldane gap closes at the critical field Hc~4T, but reopens
again at higher fields. The field dependence of the two lowest magnon modes is
experimentally studied and the results are compared with the predictions of
several theoretical models. We conclude that of several existing theories, only
the recently proposed model [Zheludev et al., cond-mat/0301424 ] is able to
reproduce all the features observed experimentally for different field
orientations.Comment: 11 pages 8 figures submitted to Phys. Rev.
Boundary conditions, the critical conductance distribution, and one-parameter scaling
Published versio
Conformal mapping methods for interfacial dynamics
The article provides a pedagogical review aimed at graduate students in
materials science, physics, and applied mathematics, focusing on recent
developments in the subject. Following a brief summary of concepts from complex
analysis, the article begins with an overview of continuous conformal-map
dynamics. This includes problems of interfacial motion driven by harmonic
fields (such as viscous fingering and void electromigration), bi-harmonic
fields (such as viscous sintering and elastic pore evolution), and
non-harmonic, conformally invariant fields (such as growth by
advection-diffusion and electro-deposition). The second part of the article is
devoted to iterated conformal maps for analogous problems in stochastic
interfacial dynamics (such as diffusion-limited aggregation, dielectric
breakdown, brittle fracture, and advection-diffusion-limited aggregation). The
third part notes that all of these models can be extended to curved surfaces by
an auxilliary conformal mapping from the complex plane, such as stereographic
projection to a sphere. The article concludes with an outlook for further
research.Comment: 37 pages, 12 (mostly color) figure
Nuclear Alpha-Particle Condensates
The -particle condensate in nuclei is a novel state described by a
product state of 's, all with their c.o.m. in the lowest 0S orbit. We
demonstrate that a typical -particle condensate is the Hoyle state
( MeV, state in C), which plays a crucial role for
the synthesis of C in the universe. The influence of antisymmentrization
in the Hoyle state on the bosonic character of the particle is
discussed in detail. It is shown to be weak. The bosonic aspects in the Hoyle
state, therefore, are predominant. It is conjectured that -particle
condensate states also exist in heavier nuclei, like O,
Ne, etc. For instance the state of O at MeV
is identified from a theoretical analysis as being a strong candidate of a
condensate. The calculated small width (34 keV) of ,
consistent with data, lends credit to the existence of heavier Hoyle-analogue
states. In non-self-conjugated nuclei such as B and C, we discuss
candidates for the product states of clusters, composed of 's,
triton's, and neutrons etc. The relationship of -particle condensation
in finite nuclei to quartetting in symmetric nuclear matter is investigated
with the help of an in-medium modified four-nucleon equation. A nonlinear order
parameter equation for quartet condensation is derived and solved for
particle condensation in infinite nuclear matter. The strong qualitative
difference with the pairing case is pointed out.Comment: 71 pages, 41 figures, review article, to be published in "Cluster in
Nuclei (Lecture Notes in Physics) - Vol.2 -", ed. by C. Beck,
(Springer-Verlag, Berlin, 2011
Interacting new agegraphic viscous dark energy with varying
We consider the new agegraphic model of dark energy with a varying
gravitational constant, , in a non-flat universe. We obtain the equation of
state and the deceleration parameters for both interacting and noninteracting
new agegraphic dark energy. We also present the equation of motion determining
the evolution behavior of the dark energy density with a time variable
gravitational constant. Finally, we generalize our study to the case of viscous
new agegraphic dark energy in the presence of an interaction term between both
dark components.Comment: 12 pages, accepted for publication in IJTP (2010
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