742 research outputs found
Next-to-leading order static gluon self-energy for anisotropic plasmas
In this paper the structure of the next-to-leading (NLO) static gluon self
energy for an anisotropic plasma is investigated in the limit of a small
momentum space anisotropy. Using the Ward identities for the static hard-loop
(HL) gluon polarization tensor and the (nontrivial) static HL vertices, we
derive a comparatively compact form for the complete NLO correction to the
structure function containing the space-like pole associated with magnetic
instabilities. On the basis of a calculation without HL vertices, it has been
conjectured that the imaginary part of this structure function is nonzero,
rendering the space-like poles integrable. We show that there are both positive
and negative contributions when HL vertices are included, highlighting the
necessity of a complete numerical evaluation, for which the present work
provides the basis.Comment: 9 pages, 2 figure
Image of Veselago lens based upon two-dimensional photonic crystal with triangular lattice
The construction of the multi-focal Veselago lens predicted earlier is
proposed on the basis of a uniaxial photonic crystal consisting of cylindrical
air holes in silicon that make a triangular lattice in a plane perpendicular to
the axis of the crystal. The object and image are in air. The period of the
crystal should be to work at the wavelength .
The lens does not provide superlensing but the half-width of the image is
. The lens is shown to have wave guiding properties depending on
the substrate material.Comment: 15 pages, 10 figure
Plasma Resonance in Layered Normal Metals and Superconductors
A microscopic theory of the plasma resonance in layered metals is presented.
It is shown that electron-impurity scattering can suppress the plasma resonance
in the normal state and sharpen it in the superconducting state. Analytic
properties of the conductivity for the electronic transport perpendicular to
the layers are investigated. The dissipative part of the electromagnetic
response in c-direction has been found to depend on frequency in a highly
non-trivial manner. This sort of behavior cannot be incorporated in the widely
used phenomenological Gorter-Kazimir model.Comment: 34 pages including 12 figures in uuencoded.file. A revised version.
Several formulas and a number of misprints are corrected. A problem with
printing of figures is fixe
Energy Gap Induced by Impurity Scattering: New Phase Transition in Anisotropic Superconductors
It is shown that layered superconductors are subjected to a phase transition
at zero temperature provided the order parameter (OP) reverses its sign on the
Fermi-surface but its angular average is finite. The transition is regulated by
an elastic impurity scattering rate . The excitation energy spectrum,
being gapless at the low level of scattering, develops a gap as soon as the
scattering rate exceeds some critical value of .Comment: Revtex, 11 page
Bose-Einstein Condensates in Strongly Disordered Traps
A Bose-Einstein condensate in an external potential consisting of a
superposition of a harmonic and a random potential is considered theoretically.
From a semi-quantitative analysis we find the size, shape and excitation
energy as a function of the disorder strength. For positive scattering length
and sufficiently strong disorder the condensate decays into fragments each of
the size of the Larkin length . This state is stable over a large
range of particle numbers. The frequency of the breathing mode scales as
. For negative scattering length a condensate of size
may exist as a metastable state. These finding are generalized to anisotropic
traps
Coulomb drag between quantum wires with different electron densities
We study the way back-scattering electron--electron interaction generates
Coulomb drag between quantum wires with different densities. At low temperature
the system can undergo a commensurate-- incommensurate transition as the
potential difference between the two wires passes a critical value
, and this transition is reflected in a marked change in the dependence
of drag resistivity on and . At high temperature a density difference
between the wires suppresses Coulomb drag induced by back scattering, and we
use the Tomonaga--Luttinger model to study this suppression in detail.Comment: 6 pages, 4 figure
Mixed Heisenberg Chains. I. The Ground State Problem
We consider a mechanism for competing interactions in alternating Heisenberg
spin chains due to the formation of local spin-singlet pairs. The competition
of spin-1 and spin-0 states reveals hidden Ising symmetry of such alternating
chains.Comment: 7 pages, RevTeX, 4 embedded eps figures, final versio
Thermodynamics of Two - Band Superconductors: The Case of MgB
Thermodynamic properties of the multiband superconductor MgB have often
been described using a simple sum of the standard BCS expressions corresponding
to - and -bands. Although, it is \textit{a priori} not clear if
this approach is working always adequately, in particular in cases of strong
interband scattering. Here we compare the often used approach of a sum of two
independent bands using BCS-like -model expressions for the specific
heat, entropy and free energy to the solution of the full Eliashberg equations.
The superconducting energy gaps, the free energy, the entropy and the heat
capacity for varying interband scattering rates are calculated within the
framework of two-band Eliashberg theory. We obtain good agreement between the
phenomenological two-band -model with the Eliashberg results, which
delivers for the first time the theoretical verification to use the
-model as a useful tool for a reliable analysis of heat capacity data.
For the thermodynamic potential and the entropy we demonstrate that only the
sum over the contributions of the two bands has physical meaning.Comment: 27 pages, 10 figures, 1 table, submitted to Phys. Rev.
Localized states and interaction induced delocalization in Bose gases with quenched disorder
Very diluted Bose gas placed into a disordered environment falls into a
fragmented localized state. At some critical density the repulsion between
particles overcomes the disorder. The gas transits into a coherent superfluid
state. In this article the geometrical and energetic characteristics of the
localized state at zero temperature and the critical density at which the
quantum phase transition from the localized to the superfluid state proceeds
are found.Comment: 17 pages, 5 figur
Hall-Effect for Neutral Atoms
It is shown that polarizable neutral systems can drift in crossed magnetic
and electric fileds. The drift velocity is perpendicular to both fields, but
contrary to the drif t velocity of a charged particle, it exists only, if
fields vary in space or in time. We develop an adiabatic theory of this
phenomenon and analyze conditions of its experimental observation. The most
proper objects for the observation of this effect are Rydberg atoms. It can be
applied for the separation of excited atoms.Comment: RevTex, 4 pages; to be published in Pis'ma v ZhET
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