2,937 research outputs found
Plasma density measurements using chirped pulse broad-band Raman amplification
Stimulated Raman backscattering is used as a non-destructive method to determine the density of plasma media at localized positions in space and time. By colliding two counter-propagating, ultra-short laser pulses with a spectral bandwidth larger than twice the plasma frequency, amplification occurs at the Stokes wavelengths, which results in regions of gain and loss separated by twice the plasma frequency, from which the plasma density can be deduced. By varying the relative delay between the laser pulses, and therefore the position and timing of the interaction, the spatio-temporal distribution of the plasma density can be mapped out
Simulation of electromagnetically and magnetically induced transparency in a magnetized plasma
Electromagnetically induced transparency (EIT), a phenomenon well known in atomic systems, has a natural analogy in a classical magnetized plasma. The magnetized plasma has a resonance for right-hand polarized electromagnetic waves at the electron cyclotron frequency Omega(0), so that a probe wave with frequency omega(1) = Omega(0) cannot propagate through the plasma. The plasma can be made transparent to such a probe by the presence of a pump wave. The pump may be an electromagnetic wave or magnetostatic wiggler. Simulations and theory show that the physical reason for the transparency is that the beating of the probe wave with the pump wave sets up a plasma oscillation, and the upper sideband of the pump wave cancels the resonant plasma current due to the probe. The theory of plasma EIT derived here extends that found in the earlier work to include the effects of the lower sideband of the pump and renormalization of the plasma frequency and an analysis of the transient response. A detailed comparison of theory to one-dimensional particle-in-cell simulations is presented and estimates for the performance ion accelerator using the EIT interaction are given. The dispersion relation and estimates for the phase velocity and amplitude of the plasma wave are in good agreement with particle-in-cell simulations.open151
Zeeman smearing of the Coulomb blockade
Charge fluctuations of a large quantum dot coupled to a two-dimensional lead
via a single-mode good Quantum Point Contact (QPC) and capacitively coupled to
a back-gate, are investigated in the presence of a parallel magnetic field. The
Zeeman term induces an asymmetry between transmission probabilities for the
spin-up and spin-down channels at the QPC, producing noticeable effects on the
quantization of the grain charge already at low magnetic fields. Performing a
quantitative analysis, I show that the capacitance between the gate and the
lead exhibits - instead of a logarithmic singularity - a reduced peak as a
function of gate voltage. Experimental applicability is discussed.Comment: 5 pages, 3 figures (Final version
Synthesizing SystemC Code from Delay Hybrid CSP
Delay is omnipresent in modern control systems, which can prompt oscillations
and may cause deterioration of control performance, invalidate both stability
and safety properties. This implies that safety or stability certificates
obtained on idealized, delay-free models of systems prone to delayed coupling
may be erratic, and further the incorrectness of the executable code generated
from these models. However, automated methods for system verification and code
generation that ought to address models of system dynamics reflecting delays
have not been paid enough attention yet in the computer science community. In
our previous work, on one hand, we investigated the verification of delay
dynamical and hybrid systems; on the other hand, we also addressed how to
synthesize SystemC code from a verified hybrid system modelled by Hybrid CSP
(HCSP) without delay. In this paper, we give a first attempt to synthesize
SystemC code from a verified delay hybrid system modelled by Delay HCSP
(dHCSP), which is an extension of HCSP by replacing ordinary differential
equations (ODEs) with delay differential equations (DDEs). We implement a tool
to support the automatic translation from dHCSP to SystemC
Critical Ising modes in low-dimensional Kondo insulators
We present an Ising-like intermediate phase for one-dimensional Kondo
insulator systems. Resulting from a spinon splitting, its low-energy
excitations are critical Ising modes, whereas the triplet sector has a spectral
gap. It should occur as long as the RKKY oscillation amplitude dominates over
any direct exchange between localized spins. The chiral fixed point, however,
becomes unstable in the far Infra-Red limit due to prevalent fluctuations among
localized spins which induce gapless triplet excitations in the spectrum. Based
on previous numerical results, we obtain a paramagnetic disordered state ruled
by the correlation length of the single impurity Kondo model.Comment: 7 pages, RevTeX; last version: to be published in Physical Review
Giant Magnetoelectric Effect in a Multiferroic Material with a High Ferroelectric Transition Temperature
We present a unique example of giant magnetoelectric effect in a conventional
multiferroic HoMnO3, where polarization is very large (~56 mC/m2) and the
ferroelectric transition temperature is higher than the magnetic ordering
temperature by an order. We attribute the uniqueness of the giant
magnetoelectric effect to the ferroelectricity induced entirely by the
off-center displacement of rare earth ions with large magnetic moments. This
finding suggests a new avenue to design multiferroics with large polarization
and higher ferroelectric transition temperature as well as large
magnetoelectric effects
Transport through a quantum dot with SU(4) Kondo entanglement
We investigate a mesoscopic setup composed of a small electron droplet (dot)
coupled to a larger quantum dot (grain) also subject to Coulomb blockade as
well as two macroscopic leads used as source and drain. An exotic Kondo ground
state other than the standard SU(2) Fermi liquid unambiguously emerges: an
SU(4) Kondo correlated liquid. The transport properties through the small dot
are analyzed for this regime, through boundary conformal field theory, and
allow a clear distinction with other regimes such as a two-channel spin state
or a two-channel orbital state.Comment: 13 pages, 3 figure
Metal-Kondo insulating transitions and transport in one dimension
We study two different metal-insulating transitions possibly occurring in
one-dimensional Kondo lattices. First, we show how doping the pure Kondo
lattice model in the strong-coupling limit, results in a Pokrovsky-Talapov
transition. This produces a conducting state with a charge susceptibility
diverging as the inverse of the doping, that seems in agreement with numerical
datas. Second, in the weak-coupling region, Kondo insulating transitions arise
due to the consequent renormalization of the backward Kondo scattering. Here,
the interplay between Kondo effect and electron-electron interactions gives
rise to significant phenomena in transport, in the high-temperature delocalized
(ballistic) regime. For repulsive interactions, as a perfect signature of Kondo
localization, the conductivity is found to decrease monotonically with
temperature. When interactions become attractive, spin fluctuations in the
electron (Luttinger-type) liquid are suddenly lowered. The latter is less
localized by magnetic impurities than for the repulsive counterpart, and as a
result a large jump in the Drude weight and a maximum in the conductivity arise
in the entrance of the Kondo insulating phase. These can be viewed as remnants
of s-wave superconductivity arising for attractive enough interactions.
Comparisons with transport in the single impurity model are also performed. We
finally discuss the case of randomly distributed magnetic defects, and the
applications on persistent currents of mesoscopic rings.Comment: 21 pages, two columns, 5 figures and 1 table; Final version: To
appear in Physical Review
Fabrication of high performance MgB2 wires by an internal Mg diffusion process
We succeeded in the fabrication of high-Jc MgB2/Fe wires applying the
internal Mg diffusion (IMD) process with pure Mg core and SiC addition. A pure
Mg rod with 2 mm diameter was placed at the center of a Fe tube, and the space
between Mg and Fe tube was filled with B powder or the powder mixture of
B-(5mol%)SiC. The composite was cold worked into 1.2mm diameter wire and
finally heat treated at temperatures above the melting point of Mg(~650oC).
During the heat treatment liquid Mg infiltrated into B layer and reacted with B
to form MgB2. X-ray diffraction analysis indicated that the major phase in the
reacted layer is MgB2. SEM analysis shows that the density of MgB2 layer is
higher than that of usual powder-in-tube(PIT) processed wires. The wires with
5mol% SiC addition heat treated at 670oC showed Jc values higher than 105A/cm2
in 8T and 41,000A/cm2 in 10T at 4.2K. These values are much higher than those
of usual PIT processed wires even compared to the ones with SiC addition.
Higher density of MgB2 layer obtained by the diffusion reaction is the major
cause of this excellent Jc values.Comment: 7page, 6figure
The electron lifetime in Luttinger liquids
We investigate the decoherence of the electron wavepacket in purely ballistic
one-dimensional systems described through the Luttinger liquid (LL). At a
finite temperature and long times , we show that the electron Green's
function for a fixed wavevector close to one Fermi point decays as
, as opposed to the power-law behavior occurring at short
times, and the emerging electron lifetime obeys for
spinful as well as spinless electrons. For strong interactions, , reflecting that the electron is not a good Landau quasiparticle in LLs. We
justify that fractionalization is the main source of electron decoherence for
spinful as well as spinless electrons clarifying the peculiar electron mass
renormalization close to the Fermi points. For spinless electrons and weak
interactions, our intuition can be enriched through a diagrammatic approach or
Fermi Golden rule and through a Johnson-Nyquist noise picture. We stress that
the electron lifetime (and the fractional quasiparticles) can be revealed from
Aharonov-Bohm experiments or momentum resolved tunneling. We aim to compare the
results with those of spin-incoherent and chiral LLs.Comment: 20 pages, 1 column, 6 figures, 1 Table; expands cond-mat/0110307 and
cond-mat/0503652; final version to appear in PR
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