771 research outputs found
Electron-Electron Interaction in Linear Arrays of Small Tunnel Junctions
We have calculated the spatial distribution of the electrostatic potential
created by an unbalanced charge in one of the conducting electrodes of a
long, uniform, linear array of small tunnel junctions. The distribution
describes, in particular, the shape of a topological single-electron soliton in
such an array. An analytical solution obtained for a circular cross section
model is compared with results of geometrical modeling of a more realistic
structure with square cross section. These solutions are very close to one
another, and can be reasonably approximated by a simple phenomenological
expression. In contrast to the previously accepted exponential approximation,
the new result describes the crossover between the linear change of the
potential near the center of the soliton to the unscreened Coulomb potential
far from the center, with an unexpected ``hump'' near the crossover point.Comment: 8 pages, RevTeX 3.0, 4 PostScript figures. To appear in Applied
Physics Letters, circa 12 Nov 199
CMOL: Second Life for Silicon?
This report is a brief review of the recent work on architectures for the
prospective hybrid CMOS/nanowire/ nanodevice ("CMOL") circuits including
digital memories, reconfigurable Boolean-logic circuits, and mixed-signal
neuromorphic networks. The basic idea of CMOL circuits is to combine the
advantages of CMOS technology (including its flexibility and high fabrication
yield) with the extremely high potential density of molecular-scale
two-terminal nanodevices. Relatively large critical dimensions of CMOS
components and the "bottom-up" approach to nanodevice fabrication may keep CMOL
fabrication costs at affordable level. At the same time, the density of active
devices in CMOL circuits may be as high as 1012 cm2 and that they may provide
an unparalleled information processing performance, up to 1020 operations per
cm2 per second, at manageable power consumption.Comment: Submitted on behalf of TIMA Editions
(http://irevues.inist.fr/tima-editions
Quantum phase slip interference device based on superconducting nanowire
We propose a transistor-like circuit including two serially connected
segments of a narrow superconducting nanowire joint by a wider segment with a
capacitively coupled gate in between. This circuit is made of amorphous NbSi
film and embedded in a network of on-chip Cr microresistors ensuring a
sufficiently high external electromagnetic impedance. Assuming a virtual regime
of quantum phase slips (QPS)in two narrow segments of the wire, leading to
quantum interference of voltages on these segments, this circuit is dual to the
dc SQUID. Our samples demonstrated appreciable Coulomb blockade voltage (analog
of critical current of the SQUIDs) and periodic modulation of this blockade by
an electrostatic gate (analog of flux modulation in the SQUIDs). The model of
this QPS transistor is discussed.Comment: 5 pages including 3 figures; in v2 the title was updated, typos were
fixed and 4 references adde
Supercurrent fluctuations in short filaments
We evaluate the average and the standard deviation of the supercurrent in
superconducting nanobridges, as functions of the temperature and the phase
difference, in an equilibrium situation. We also evaluate the autocorrelation
of the supercurrent as a function of the elapsed time. The behavior of
supercurrent fluctuations is qualitatively different from from that of the
normal current: they depend on the phase difference, have a different
temperature dependence, and for appropriate range their standard deviation is
independent of the probing time. We considered two radically different
filaments and obtained very similar results for both. Fluctuations of the
supercurrent can in principle be measured
Statistics of voltage fluctuations in resistively shunted Josephson junctions
The intrinsic nonlinearity of Josephson junctions converts Gaussian current
noise in the input into non-Gaussian voltage noise in the output. For a
resistively shunted Josephson junction with white input noise we determine
numerically exactly the properties of the few lowest cumulants of the voltage
fluctuations, and we derive analytical expressions for these cumulants in
several important limits. The statistics of the voltage fluctuations is found
to be Gaussian at bias currents well above the Josephson critical current, but
Poissonian at currents below the critical value. In the transition region close
to the critical current the higher-order cumulants oscillate and the voltage
noise is strongly non-Gaussian. For coloured input noise we determine the third
cumulant of the voltage.Comment: 9 pages, 5 figure
Possible cooling by resonant Fowler-Nordheim emission
A new method of electronic refrigeration based on resonant Fowler-Nordheim
emission is proposed and analyzed. In this method, a bulk emitter is covered
with a-few-nm-thick film of a widegap semiconductor, creating an intermediate
step between electron energies in the emitter and in vacuum. An external
electric field tilts this potential profile, forming a quantum well, and hence
2D electron subbands at the semiconductor-vacuum boundary. Alignment of the
lowest subband with the energy levels of the hottest electrons of the emitter
(a few above its Fermi level) leads to a resonant, selective emission
of these electrons, providing emitter cooling. Calculations show that cooling
power as high as 10^{4} W/cm^{2} (at 300 K), and temperatures down to 10 K may
be achieved using this effect.Comment: 4 pages, 2 figure
Single-Electron Parametron: Reversible Computation in a Discrete State System
We have analyzed energy dissipation in a digital device (``Single-Electron
Parametron'') in which discrete degrees of freedom are used for presenting
digital information. If the switching speed is not too high, the device may
operate reversibly (adiabatically), and the energy dissipation per
bit may be much less than the thermal energy . The energy-time product
is, however, much larger than Planck's constant , at
least in the standard ``orthodox'' model of single-electron tunneling, which
was used in our calculations.Comment: 9 pages, RevTex, 3 figure
Quasi-adiabatic Switching for Metal-Island Quantum-dot Cellular Automata
Recent experiments have demonstrated a working cell suitable for implementing
the Quantum-dot Cellular Automata (QCA) paradigm. These experiments have been
performed using metal island clusters. The most promising approach to QCA
operation involves quasi-adiabatically switching the cells. This has been
analyzed extensively in gated semiconductor cells. Here we present a metal
island cell structure that makes quasi-adiabatic switching possible. We show
how this permits quasi-adiabatic clocking, and enables a pipelined
architecture.Comment: 40 preprint-style double-spaced pages including 16 figure
Magnetic Sensors Based on Long Josephson Tunnel Junctions - An Alternative to SQUIDs
The properties of Josephson devices are strongly affected by geometrical
effects. A loop-shaped superconducting electrode tightly couples a long
Josephson tunnel junction with the surrounding electromagnetic field. Due to
the fluxoid conservation, any change of the magnetic flux linked to the loop
results in a variation of the shielding current circulating around the loop,
which, in turn, affects the critical current of the Josephson junction. This
method allows the realization of a novel family of robust superconducting
devices (not based on the quantum interference) which can function as a
general-purpose magnetic sensors. The best performance is accomplished without
compromising the noise performance by employing an in-line-type junction few
times longer than its Josephson penetration length. The linear (rather than
periodic) response to magnetic flux changes over a wide range is just one of
its several advantages compared to the most sensitive magnetic detectors
currently available, namely the Superconducting Quantum Interference Devices
(SQUID). We will also comment on the drawbacks of the proposed system and
speculate on its noise properties.Comment: 13 pages, 4 figure
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