401 research outputs found
Nonlocal effects in the shot noise of diffusive superconductor - normal-metal systems
A cross-shaped diffusive system with two superconducting and two normal
electrodes is considered. A voltage is applied between the normal
leads. Even in the absence of average current through the superconducting
electrodes their presence increases the shot noise at the normal electrodes and
doubles it in the case of a strong coupling to the superconductors. The
nonequilibrium noise at the superconducting electrodes remains finite even in
the case of a vanishingly small transport current due to the absence of energy
transfer into the superconductors. This noise is suppressed by
electron-electron scattering at sufficiently high voltages.Comment: 4 pages, RevTeX, 2 eps figure
Design and cryogenic operation of a hybrid quantum-CMOS circuit
Silicon-On-Insulator nanowire transistors of very small dimensions exhibit
quantum effects like Coulomb blockade or single-dopant transport at low
temperature. The same process also yields excellent field-effect transistors
(FETs) for larger dimensions, allowing to design integrated circuits. Using the
same process, we have co-integrated a FET-based ring oscillator circuit
operating at cryogenic temperature which generates a radio-frequency (RF)
signal on the gate of a nanoscale device showing Coulomb oscillations. We
observe rectification of the RF signal, in good agreement with modeling
Positive cross-correlations induced by ferromagnetic contacts
Due to the Fermionic nature of carriers, correlations between electric
currents flowing through two different contacts attached to a conductor present
a negative sign. Possibility for positive cross-correlations has been
demonstrated in hybrid normal/superconductor structures under certain
conditions. In this paper we show that positive cross-correlations can be
induced, if not already present, in such structures by employing ferromagnetic
leads with magnetizations aligned anti-parallel to each other. We consider
three-terminal hybrid structures and calculate the mean-square correlations of
current fluctuations as a function of the bias voltage at finite temperature.Comment: 6 pages, 5 figures; accepted version by PRB, figures replace
Viral and bacterial contamination of shellfish harvested in the natural environment
Fecal coliforms, Salmonella and antigens linked to hepatitis A virus were searched for in shellfish collected in farms or natural beds along the French coast. Statistical analysis was performed on 176 test samples harvested at 8 different stations. For fecal coliforms, there were significant statistical differences between stations (F = 44.39; p < 0.001). Salmonella was found more frequently in 2 of the stations and was isolated more often in stations where mean fecal coliform contamination was high. The presence of antigens linked to hepatitis A virus was low (detection in only 2 stations where mean fecal coliform contamination was also low). No relation between viral and bacterial markers was observed at any of the stations
Full Current Statistics in Diffusive Normal-Superconductor Structures
We study the current statistics in normal diffusive conductors in contact
with a superconductor. Using an extension of the Keldysh Green's function
method we are able to find the full distribution of charge transfers for all
temperatures and voltages. For the non-Gaussian regime, we show that the
equilibrium current fluctuations are enhanced by the presence of the
superconductor. We predict an enhancement of the nonequilibrium current noise
for temperatures below and voltages of the order of the Thouless energy
E_Th=D/L^2. Our calculation fully accounts for the proximity effect in the
normal metal and agrees with experimental data. We demonstrate that the
calculation of the full current statistics is in fact simpler than a concrete
calculation of the noise.Comment: 4 pages, 2 figures (included
Defect detection in nano-scale transistors based on radio-frequency reflectometry
Radio-frequency reflectometry in silicon single-electron transistors (SETs)
is presented. At low temperatures (<4 K), in addition to the expected Coulomb
blockade features associated with charging of the SET dot, quasi-periodic
oscillations are observed that persist in the fully depleted regime where the
SET dot is completely empty. A model, confirmed by simulations, indicates that
these oscillations originate from charging of an unintended floating gate
located in the heavily doped polycrystalline silicon gate stack. The technique
used in this experiment can be applied for detailed spectroscopy of various
charge defects in nanoscale SETs and field effect transistorsComment: 3 pages, 3 figure
Energy dependent counting statistics in diffusive superconducting tunnel junctions
We present an investigation of the energy dependence of the full charge
counting statistics in diffusive
normal-insulating-normal-insulating-superconducting junctions. It is found that
the current in general is transported via a correlated transfer of pairs of
electrons. Only in the case of strongly asymmetric tunnel barriers or energies
much larger than the Thouless energy is the pair transfer uncorrelated. The
second cumulant, the noise, is found to depend strongly on the applied voltage
and temperature. For a junction resistance dominated by the tunnel barrier to
the normal reservoir, the differential shot noise shows a double peak feature
at voltages of the order of the Thouless energy, a signature of an ensemble
averaged electron-hole resonance.Comment: 8 pages, 5 figure
Nonlinear shot noise in mesoscopic diffusive normal-superconducting systems
We study differential shot noise in mesoscopic diffusive
normal-superconducting (NS) heterostructures at finite voltages where nonlinear
effects due to the superconducting proximity effect arise. A numerical
scattering-matrix approach is adopted. Through an NS contact, we observe that
the shot noise shows a reentrant dependence on voltage due to the
superconducting proximity effect but the differential Fano factor stays
approximately constant. Furthermore, we consider differential shot noise in the
structures where an insulating barrier is formed between normal and
superconducting regions and calculate the differential Fano factor as a
function of barrier height.Comment: 4 pages, 6 figure
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