9,806 research outputs found
Stimulated Raman backscattering of laser radiation in deep plasma channels
Stimulated Raman backscattering (RBS) of intense laser radiation confined by
a single-mode plasma channel with a radial variation of plasma frequency
greater than a homogeneous-plasma RBS bandwidth is characterized by a strong
transverse localization of resonantly-driven electron plasma waves (EPW). The
EPW localization reduces the peak growth rate of RBS and increases the
amplification bandwidth. The continuum of non-bound modes of backscattered
radiation shrinks the transverse field profile in a channel and increases the
RBS growth rate. Solution of the initial-value problem shows that an
electromagnetic pulse amplified by the RBS in the single-mode deep plasma
channel has a group velocity higher than in the case of homogeneous-plasma
Raman amplification. Implications to the design of an RBS pulse compressor in a
plasma channel are discussed.Comment: 11 pages, 3 figures; submitted to Physics of Plasma
Full counting statistics of a charge pump in the Coulomb blockade regime
We study the full charge counting statistics of a charge pump based on a
nearly open single electron transistor. The problem is mapped onto an exactly
soluble problem of a g=1/2 non-equilibrium Luttinger liquid with an impurity.
We obtain an analytic expression for the generating function of the transmitted
charge for an arbitrary pumping strength. Even though this model contains
fractionally charged excitations only integer transmitted charges can be
observed during finite observation times.Comment: 4 pages, 1 figur
Andreev tunneling through a double quantum-dot system coupled to a ferromagnet and a superconductor: effects of mean field electronic correlations
We study the transport properties of a hybrid nanostructure composed of a
ferromagnet, two quantum dots, and a superconductor connected in series. By
using the non-equilibrium Green's function approach, we have calculated the
electric current, the differential conductance and the transmittance for
energies within the superconductor gap. In this regime, the mechanism of charge
transmission is the Andreev reflection, which allows for a control of the
current through the ferromagnet polarization. We have also included interdot
and intradot interactions, and have analyzed their influence through a mean
field approximation. In the presence of interactions, Coulomb blockade tend to
localized the electrons at the double-dot system, leading to an asymmetric
pattern for the density of states at the dots, and thus reducing the
transmission probability through the device. In particular, for non-zero
polarization, the intradot interaction splits the spin degeneracy, reducing the
maximum value of the current due to different spin-up and spin-down densities
of states. Negative differential conductance (NDC) appears for some regions of
the voltage bias, as a result of the interplay of the Andreev scattering with
electronic correlations. By applying a gate voltage at the dots, one can tune
the effect, changing the voltage region where this novel phenomenon appears.
This mechanism to control the current may be of importance in technological
applications.Comment: 12 pages, 11 figure
Massive Fields and the 2D String
The first massive level of closed bosonic string theory is studied.
Free-field equations are derived by imposing Weyl invariance on the world
sheet. A two-parameter solution to the equation of motion and constraints is
found in two dimensions with a flat linear-dilaton background. One-to-one
tachyon scattering is studied in this background. The results support Dhar,
Mandal and Wadia's proposal that 2D critical string theory corresponds to the
c=1 matrix model in which both sides of the Fermi sea are excited.Comment: 17 pages, Latex. V2: One ref added, minor rephrasing of the first
paragraph in Sec.3.1, typos in (56) and (57) correcte
Estimation of the particle-antiparticle correlation effect for pion production in heavy ion collisions
Estimation of the back-to-back pi-pi correlations arising due to evolution of
the pionic field in the course of pion production process is given for central
heavy nucleus collisions at moderate energies.Comment: 6 LaTeX pages + 5 ps figure
Tunneling into d-wave superconductors: Effects of interface spin-orbit coupling
Tunneling conductance of a clean normal metal/d-wave superconductor junction
is studied by using the extended Blonder-Tinkham-Klapwijk formalism. We show
that the conductance is significantly affected by the interface spin-orbit
coupling of the Rashba type, which is inevitably present due to the asymmetry
of the junction.Comment: 4 pages, 4 figure
Observability of a projected new state of matter: a metallic superfluid
Dissipationless quantum states, such as superconductivity and superfluidity,
have attracted interest for almost a century. A variety of systems exhibit
these macroscopic quantum phenomena, ranging from superconducting electrons in
metals to superfluid liquids, atomic vapours, and even large nuclei. It was
recently suggested that liquid metallic hydrogen could form two new unusual
dissipationless quantum states, namely the metallic superfluid and the
superconducting superfluid. Liquid metallic hydrogen is projected to occur only
at an extremely high pressure of about 400 GPa, while pressures on hydrogen of
320 GPa having already been reported. The issue to be adressed is if this state
could be experimentally observable in principle. We propose four experimental
probes for detecting it.Comment: in print in Phys. Rev. Let
Nonlinear Hysteretic Torsional Waves
We theoretically study and experimentally report the propagation of nonlinear
hysteretic torsional pulses in a vertical granular chain made of cm-scale,
self-hanged magnetic beads. As predicted by contact mechanics, the torsional
coupling between two beads is found nonlinear hysteretic. This results in a
nonlinear pulse distortion essentially different from the distortion predicted
by classical nonlinearities, and in a complex dynamic response depending on the
history of the wave particle angular velocity. Both are consistent with the
predictions of purely hysteretic nonlinear elasticity and the
Preisach-Mayergoyz hysteresis model, providing the opportunity to study the
phenomenon of nonlinear dynamic hysteresis in the absence of other type of
material nonlinearities. The proposed configuration reveals a plethora of
interesting phenomena including giant amplitude-dependent attenuation, short
term memory as well as dispersive properties. Thus, it could find interesting
applications in nonlinear wave control devices such as strong
amplitude-dependent filters
Normal metal - superconductor tunnel junction as a Brownian refrigerator
Thermal noise generated by a hot resistor (resistance ) can, under proper
conditions, catalyze heat removal from a cold normal metal (N) in contact with
a superconductor (S) via a tunnel barrier. Such a NIS junction acts as
Maxwell's demon, rectifying the heat flow. Upon reversal of the temperature
gradient between the resistor and the junction the heat fluxes are reversed:
this presents a regime which is not accessible in an ordinary voltage-biased
NIS structure. We obtain analytical results for the cooling performance in an
idealized high impedance environment, and perform numerical calculations for
general . We conclude by assessing the experimental feasibility of the
proposed effect
Mesoscopic Casimir forces from effects of discrete particle number in the quantum vacuum
Traditionally it is assumed that the Casimir vacuum pressure does not depend
on the ultraviolet cut-off. There are, however, some arguments that the effect
actually depends on the regularization procedure and thus on the
trans-Planckian physics. We provide the condensed matter example where the
Casimir forces do explicitly depend on the microscopic (correspondingly
trans-Planckian) physics due to the mesoscopic finite-N effects, where N is the
number of bare particles in condensed matter (or correspondingly the number of
the elements comprising the quantum vacuum). The finite-N effects lead to
mesoscopic fluctuations of the vacuum pressure. The amplitude of the mesoscopic
flustuations of the Casimir force in a system with linear dimension L is larger
by the factor N^{1/3}\sim L/a than the traditional value of the Casimir force
given by effective theory, where a is the interatomic distance which plays the
role of the Planck length.Comment: LaTeX file, 13 pages, no figures, submitted to JETP Letter
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