226 research outputs found
Supercurrent noise in quantum point contacts
Spectral density of current fluctuations in a short ballistic superconducting
quantum point contact is calculated for arbitrary bias voltages . Contrary
to a common opinion that the supercurrent flow in Josephson junctions is
coherent process with no fluctuations, we find extremely large current noise
that is {\em caused} by the supercurrent coherence. An unusual feature of the
noise, besides its magnitude, is its voltage dependence: the noise decreases
with increasing , despite the fact that the dc current grows steadily with
. At finite voltages the noise can be qualitatively understood as the shot
noise of the large charge quanta of magnitude equal to the charge
transferred during one period of Josephson oscillations.Comment: 12 pages, revtex, 2 figures by fax/conventional mail upon reques
Proposal For A Quantum Hall Pump
A device is proposed that is similar in spirit to the electron turnstile
except that it operates within a quantum Hall fluid. In the integer quantum
Hall regime, this device pumps an integer number of electrons per cycle. In the
fractional regime, it pumps an integer number of fractionally charged
quasiparticles per cycle. It is proposed that such a device can make an
accurate measurement of the charge of the quantum Hall effect quasiparticles.Comment: 4 pages, LaTeX, 4 figures include
Nonuniversal behavior of scattering between fractional quantum Hall edges
Among the predicted properties of fractional quantum Hall states are
fractionally charged quasiparticles and conducting edge-states described as
chiral Luttinger liquids. In a system with a narrow constriction, tunneling of
quasi-particles between states at different edges can lead to resistance and to
shot noise. The ratio of the shot noise to the backscattered current, in the
weak scattering regime, measures the fractional charge of the quasi-particle,
which has been confirmed in several experiments. However, the non-linearity of
the resistance predicted by the chiral Luttinger liquid theory was apparently
not observed in some of these cases. As a possible explanation for these
discrepancies, we consider a model where a smooth edge profile leads to
formation of additional edge states. Coupling between the current carrying edge
mode and the additional phonon like mode can lead to {\it nonuniversal}
exponents in the current-voltage characteristic, while preserving the ratio
between shot noise and the back-scattered current, for weak backscattering. For
special values of the coupling, one may obtain a linear I-V behavior.Comment: 10 pages, 3 figure
~115 GeV and ~143 GeV Higgs mass considerations within the Composite Particles Model
The radiatively generated Higgs mass is obtained by requiring that leading
"divergences" are cancelled in both 2D and 4D. This predicts one or more viable
modes; the k=1 mode mass is m_H\cong2/3 m_t\cong115GeV whereas the k=2 mode is
m_H\cong143GeV. These findings are interpreted within the Composite Particles
Model (CPM), [Popovic 2002, 2010], with the massive top quark being a composite
structure composed of 3 fundamental O quarks (O\bar{O}O) and the massive Higgs
scalar being a color-neutral meson like structure composed of 2 fundamental O
quarks (\bar{O}O). The CPM predicts that the Z mass generation is mediated
primarily by a top - anti top whereas the Higgs mass is generated primarily by
a O - anti O interactions. The relationship [Popovic 2010] between top Yukawa
coupling and strong QCD coupling, obtained by requiring that top - anti top
channel is neither attractive or repulsive at tree level at \surd s\congM_Z,
defines the Z mass. In addition, this relationship indirectly defines the
electroweak symmetry breaking (EWSB) vacuum expectation value (VEV), the CPM
Higgs mass and potentially the EWSB scale.Comment: 11 pages, 3 figures, slightly updated second version: Lagrangian
explicitly specified, OOO->O\bar{O}O and a few other typos correcte
Drag on particles in a nematic suspension by a moving nematic-isotropic interface
We report the first clear demonstration of drag on colloidal particles by a moving nematic-isotropic
interface. The balance of forces explains our observation of periodic, strip-like structures that are produced by the movement of these particles
Shot noise suppression at room temperature in atomic-scale Au junctions
Shot noise encodes additional information not directly inferable from simple
electronic transport measurements. Previous measurements in atomic-scale metal
junctions at cryogenic temperatures have shown suppression of the shot noise at
particular conductance values. This suppression demonstrates that transport in
these structures proceeds via discrete quantum channels. Using a high frequency
technique, we simultaneously acquire noise data and conductance histograms in
Au junctions at room temperature and ambient conditions. We observe noise
suppression at up to three conductance quanta, with possible indications of
current-induced local heating and noise in the contact region at high
biases. These measurements demonstrate the quantum character of transport at
room temperature at the atomic scale. This technique provides an additional
tool for studying dissipation and correlations in nanodevices.Comment: 15 pages, 4 figures + supporting information (6 pages, 6 figures
Low frequency admittance of a quantum point contact
We present a current and charge conserving theory for the low frequency
admittance of a quantum point contact. We derive expressions for the
electrochemical capacitance and the displacement current. The latter is
determined by the {\em emittance} which equals the capacitance only in the
limit of vanishing transmission. With the opening of channels the capacitance
and the emittance decrease in a step-like manner in synchronism with the
conductance steps. For vanishing reflection, the capacitance vanishes and the
emittance is negative.Comment: 11 pages, revtex file, 2 ps figure
Analyzing powers Ayy, Axx, Axz and Ay in the dd->3Hen reaction at 270 MeV
The data on the tensor Ayy, Axx, Axz and vector Ay analyzing powers in the
dd->3Hen obtained at Td= 270 MeV in the angular range 0 - 110 degrees in the
c.m. are presented. The observed negative sign of the tensor analyzing powers
Ayy, Axx and Axz at small angles clearly demonstrate the sensitivity to the
ratio of the D and S wave component of the 3He wave function. However, the
one-nucleon exchange calculations by using the standard 3He wave functions have
failed to reproduce the strong variation of the tensor analyzing powers as a
function of the angle in the c.m.Comment: 8 pages, 7 figures, 4 tables. Submitted to EPJ
Analysis of Shot Noise at Finite Temperatures in Fractional Quantum Hall Edge States
We investigate shot noise at {\it finite temperatures} induced by the
quasi-particle tunneling between fractional quantum Hall (FQH) edge states. The
resulting Fano factor has the peak structure at a certain bias voltage. Such a
structure indicates that quasi-particles are weakly {\it glued} due to thermal
fluctuation. We show that the effect makes it possible to probe the difference
of statistics between FQH states where quasi-particles have the
same unit charge.Finally we propose a way to indirectly obtain statistical
angle in hierarchical FQH states.Comment: 5 pages, 3 figure
Tensor analyzing power Ayy in deuteron inclusive breakup at large Pt and spin structure of deuteron at short internucleonic distances
The Ayy data for deuteron inclusive breakup off hydrogen and carbon at a
deuteron momentum of 9.0 GeV/c and large Pt of emitted protons are presented.
The large values of Ayy independent of the target mass reflect the sensitivity
of the data to the deuteron spin structure. The data obtained at fixed and
plotted versus Pt clearly demonstrate the dependence of the deuteron spin
structure at short internucleonic distances on two variables. The data are
compared with the calculations using Paris, CD-Bonn and Karmanov's deuteron
wave functions.Comment: 4 pages, 2 figures, talk given at the SPIN2004 Conf., 10-16 Oct.
2004, Triest, Ital
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