20 research outputs found
One and two dimensional tunnel junction arrays in weak Coulomb blockade regime-absolute accuracy in thermometry
We have investigated one and two dimensional (1D and 2D) arrays of tunnel
junctions in partial Coulomb blockade regime. The absolute accuracy of the
Coulomb blockade thermometer is influenced by the external impedance of the
array, which is not the same in the different topologies of 1D and 2D arrays.
We demonstrate, both by experiment and by theoretical calculations in simple
geometries, that the 1D structures are better in this respect. Yet in both 1D
and 2D, the influence of the environment can be made arbitrarily small by
making the array sufficiently large.Comment: 11 pages, 3 figure
Coulomb blockade in one-dimensional arrays of high conductance tunnel junctions
Properties of one-dimensional (1D) arrays of low Ohmic tunnel junctions (i.e.
junctions with resistances comparable to, or less than, the quantum resistance
k) have been studied experimentally
and theoretically. Our experimental data demonstrate that -- in agreement with
previous results on single- and double-junction systems -- Coulomb blockade
effects survive even in the strong tunneling regime and are still clearly
visible for junction resistances as low as 1 k. We have developed a
quasiclassical theory of electron transport in junction arrays in the strong
tunneling regime. Good agreement between the predictions of this theory and the
experimental data has been observed. We also show that, due to both heating
effects and a relatively large correction to the linear relation between the
half-width of the conductance dip around zero bias voltage, , and the
measured electronic temperature, such arrays are inferior to those
conventionally used in the Coulomb Blockade Thermometry (CBT). Still, the
desired correction to the half-width, , can be determined
rather easily and it is proportional to the magnitude of the conductance dip
around zero bias voltage, . The constant of proportionality is a
function of the ratio of the junction and quantum resistances, ,
and it is a pure strong tunneling effect.Comment: LaTeX file + five postscript figure
Atomic layer deposition of ZnS nanotubes
We report on growth of high-aspect-ratio () zinc sulfide
nanotubes with variable, precisely tunable, wall thicknesses and tube diameters
into highly ordered pores of anodic alumina templates by atomic layer
deposition (ALD) at temperatures as low as 75 C. Various
characterization techniques are employed to gain information on the
composition, morphology, and crystal structure of the synthesized samples.
Besides practical applications, the ALD-grown tubes could be envisaged as model
systems for the study of a certain class of size-dependent quantum and
classical phenomena.Comment: 1 LaTeX source file, 8 eps figures, and the manuscript in PDF forma
Single-charge escape processes through a hybrid turnstile in a dissipative environment
We have investigated the static, charge-trapping properties of a hybrid
superconductor---normal metal electron turnstile embedded into a high-ohmic
environment. The device includes a local Cr resistor on one side of the
turnstile, and a superconducting trapping island on the other side. The
electron hold times, t ~ 2-20s, in our two-junction circuit are comparable with
those of typical multi-junction, N >= 4, normal-metal single-electron tunneling
devices. A semi-phenomenological model of the environmental activation of
tunneling is applied for the analysis of the switching statistics. The
experimental results are promising for electrical metrology.Comment: Submitted to New Journal of Physics 201
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
Effect of quantum noise on Coulomb blockade in normal tunnel junctions at high voltages
We have investigated asymptotic behavior of normal tunnel junctions at
voltages where even the best ohmic environments start to look like RC
transmission lines. In the experiments, this is manifested by an exceedingly
slow approach to the linear behavior above the Coulomb gap. As expected on the
basis of the quantum theory taking into account interaction with the
environmental modes, better fits are obtained using 1/sqrt{V}- than 1/V-
dependence for the asymptote. These results agree with the horizon picture if
the frequency-dependent phase velocity is employed instead of the speed of
light in order to determine the extent of the surroundings seen by the
junction.Comment: 9 pages, 4 figures, submitted to Phys. Rev.
Comparison of Coulomb Blockade Thermometers with the International Temperature Scale PLTS-2000
The operation of the primary Coulomb blockade thermometer (CBT) is based on a
measurement of bias voltage dependent conductance of arrays of tunnel junctions
between normal metal electrodes. Here we report on a comparison of a CBT with a
high accuracy realization of the PLTS-2000 temperature scale in the range from
0.008 K to 0.65 K. An overall agreement of about 1% was found for temperatures
above 0.25 K. For lower temperatures increasing differences are caused by
thermalization problems which are accounted for by numerical calculations based
on electron-phonon decoupling.Comment: 6 pages, 5 figure
Electron transport through interacting quantum dots
We present a detailed theoretical investigation of the effect of Coulomb
interactions on electron transport through quantum dots and double barrier
structures connected to a voltage source via an arbitrary linear impedance.
Combining real time path integral techniques with the scattering matrix
approach we derive the effective action and evaluate the current-voltage
characteristics of quantum dots at sufficiently large conductances. Our
analysis reveals a reach variety of different regimes which we specify in
details for the case of chaotic quantum dots. At sufficiently low energies the
interaction correction to the current depends logarithmically on temperature
and voltage. We identify two different logarithmic regimes with the crossover
between them occurring at energies of order of the inverse dwell time of
electrons in the dot. We also analyze the frequency-dependent shot noise in
chaotic quantum dots and elucidate its direct relation to interaction effects
in mesoscopic electron transport.Comment: 21 pages, 4 figures. References added, discussion slightly extende
Charging Ultrasmall Tunnel Junctions in Electromagnetic Environment
We have investigated the quantum admittance of an ultrasmall tunnel junction
with arbitrary tunneling strength under an electromagnetic environment. Using
the functional integral approach a close analytical expression of the quantum
admittance is derived for a general electromagnetic environment. We then
consider a specific controllable environment where a resistance is connected in
series with the tunneling junction, for which we derived the dc quantum
conductance from the zero frequency limit of the imaginary part of the quantum
admittance. For such electromagnetic environment the dc conductance has been
investigated in recent experiments, and our numerical results agree
quantitatively very well with the measurements. Our complete numerical results
for the entire range of junction conductance and electromagnetic environmental
conductance confirmed the few existing theoretical conclusions.Comment: 7 pages, 3 ps-figure
Current Fluctuations and Electron-Electron Interactions in Coherent Conductors
We analyze current fluctuations in mesoscopic coherent conductors in the
presence of electron-electron interactions. In a wide range of parameters we
obtain explicit universal dependencies of the current noise on temperature,
voltage and frequency. We demonstrate that Coulomb interaction decreases the
Nyquist noise. In this case the interaction correction to the noise spectrum is
governed by the combination , where is the transmission
of the -th conducting mode. The effect of electron-electron interactions on
the shot noise is more complicated. At sufficiently large voltages we recover
two different interaction corrections entering with opposite signs. The net
result is proportional to , i.e. Coulomb interaction
decreases the shot noise at low transmissions and increases it at high
transmissions.Comment: 16 pages, 2 figure