878 research outputs found
Hierarchical Wigner Crystal at the Edge of Quantum Hall Bar
We show that quasiholes persist near the edge of incompressible Quantum Hall
state forming a Wigner structure. The average density of quasiholes is fixed by
electrostatics and decreases slowly with increasing distance from the edge. As
we see from elementary reasoning, their specific arrangement can not be a
regular Wigner lattice and shows a complex hierarchical structure of
dislocations.Comment: LaTEX file. Ps figures upon reques
Voltage-induced Shapiro steps in a superconducting multi-terminal structure
When a superconducting tunnel junction at a finite voltage is irradiated with
microwaves, the interplay between the alternating Josephson current and the ac
field gives rise to steps in the dc current known as Shapiro steps. In this
work we predict that in a mesoscopic structure connected to several
superconducting terminals one can induce Shapiro-like steps in the absence of
any external radiation simply by tuning the voltages of the leads. To
illustrate this effect we make quantitative predictions for a three-terminal
structure which comprises a diffusive superconductor-normal
metal-superconductor junction and a tunneling probe, a set-up which can be
realized experimentally.Comment: revtex4, 5 pages, 5 figures, to appear in Phys. Rev.
Inelastic electron relaxation rates caused by Spin M/2 Kondo Impurities
We study a spin S=M/2--Kondo system coupled to electrons in an arbitrary
nonequilibrium situation above Kondo temperature. Coupling to hot electrons
leads to an increased inverse lifetime of pseudo particles, related to the
Korringa width. This in turn is responsible for the increased inelastic
relaxation rates of the electronic system. The rates are related to spin--spin
correlation functions which are determined using a projection operator
formalism. The results generalize recent findings for S=1/2--Kondo impurities
which have been used to describe energy relaxation experiments in disordered
mesoscopic wires.Comment: Brief Report, 4 page
Measuring the distribution of current fluctuations through a Josephson junction with very short current pulses
We propose to probe the distribution of current fluctuations by means of the
escape probability histogram of a Josephson junction (JJ), obtained using very
short bias current pulses in the adiabatic regime, where the low-frequency
component of the current fluctuations plays a crucial role. We analyze the
effect of the third cumulant on the histogram in the small skewness limit, and
address two concrete examples assuming realistic parameters for the JJ. In the
first one we study the effects due to fluctuations produced by a tunnel
junction, finding that the signature of higher cumulants can be detected by
taking the derivative of the escape probability with respect to current. In
such a realistic situation, though, the determination of the whole distribution
of current fluctuations requires an amplification of the cumulants. As a second
example we consider magnetic flux fluctuations acting on a SQUID produced by a
random telegraph source of noise.Comment: 6 pages, 6 figures; final versio
Non-Abelian phases, charge pumping, and quantum computation with Josephson junctions
Non-Abelian geometric phases can be generated and detected in certain
superconducting nanocircuits. Here we consider an example where the holonomies
are related to the adiabatic charge dynamics of the Josephson network. We
demonstrate that such a device can be applied both for adiabatic charge pumping
and as an implementation of a quantum computer.Comment: 11 pages RevTex, 3 figures in eps format, revised versio
Nonequilibrium Electron Distribution in Presence of Kondo Impurities
We study the energy relaxation of quasiparticles in voltage biased mesoscopic
wires in presence of magnetic impurities. The renormalization of the exchange
interaction of Kondo impurities coupled to conduction electrons is extended to
the case of a nonequilibrium electron distribution, which is determined
self-consistently from a Boltzmann equation with a collision term due to Kondo
impurity mediated electron-electron scattering. The approach leads to
predictions in quantitative agreement with recent experiments by Pothier et al.
[Phys. Rev. Lett. 79, 3490 (1997)].Comment: 4 pages, 3 figure
Occupational lead neurotoxicity: Improvement in behavioural effects after reduction of exposure.
To evaluate critical exposure levels and the reversibility of lead neurotoxicity a group of lead exposed foundry workers and an unexposed reference population were followed up for three years. During this period, tests designed to monitor neurobehavioural function and lead dose were administered. Evaluations of 160 workers during the first year showed dose dependent decrements in mood, visual/motor performance, memory, and verbal concept formation. Subsequently, an improvement in the hygienic conditions at the plant resulted in striking reductions in blood lead concentrations over the following two years. Attendant improvement in indices of tension (20% reduction), anger (18%), depression (26%), fatigue (27%), and confusion (13%) was observed. Performance on neurobehavioural testing generally correlated best with integrated dose estimates derived from blood lead concentrations measured periodically over the study period; zinc protoporphyrin levels were less well correlated with function. This investigation confirms the importance of compliance with workplace standards designed to lower exposures to ensure that individual blood lead concentrations remain below 50 micrograms/dl
Probing interactions in mesoscopic gold wires
We have measured in gold wires the energy exchange rate between
quasiparticles, the phase coherence time of quasiparticles and the resistance
vs. temperature, in order to probe the interaction processes which are relevant
at low temperatures. We find that the energy exchange rate is higher than
expected from the theory of electron-electron interactions, and that it has a
different energy dependence. The dephasing time is constant at temperatures
between 8 K and 0.5 K, and it increases below 0.5 K. The magnetoresistance is
negative at large field scales, and the resistance decreases logarithmically
with increasing temperatures, indicating the presence of magnetic impurities,
probably Fe. Whereas resistivity and phase coherence measurements can be
attributed to magnetic impurities, the question is raised whether these
magnetic impurities could also mediate energy exchanges between quasiparticles.Comment: latex pothier.tex, 12 files, 15 pages in: Proceedings of the NATO
Advanced Research Workshop on Size Dependent Magnetic Scattering, Pesc,
Hungary, May 28 - June 1st, 2000 Chandrasekhar V., Van Haesendonck C. eds
(Kluwer, 2001) [SPEC-S00/083
Frequency-Dependent Shot Noise as a Probe of Electron-Electron Interaction in Mesoscopic Diffusive Contacts
The frequency-dependent shot noise in long and narrow mesoscopic diffusive
contacts is numerically calculated. The case of arbitrarily strong
electron-electron scattering and zero temperature of electrodes is considered.
For all voltages, the noise increases with frequency and tends to finite
values. These limiting values are larger than the Poissonian noise and increase
nearly as voltage to power 4/3. This allows one to experimentally determine the
parameters of electron-electron interaction.Comment: 3 pages, RevTeX, 3 eps figure
Arrays of Josephson junctions in an environment with vanishing impedance
The Hamiltonian operator for an unbiased array of Josephson junctions with
gate voltages is constructed when only Cooper pair tunnelling and charging
effects are taken into account. The supercurrent through the system and the
pumped current induced by changing the gate voltages periodically are discussed
with an emphasis on the inaccuracies in the Cooper pair pumping.
Renormalisation of the Hamiltonian operator is used in order to reliably
parametrise the effects due to inhomogeneity in the array and non-ideal gating
sequences. The relatively simple model yields an explicit, testable prediction
based on three experimentally motivated and determinable parameters.Comment: 13 pages, 9 figures, uses RevTeX and epsfig, Revised version, Better
readability and some new result
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