80 research outputs found
Single Flux Transistor: the controllable interplay of Coherent Quantum Phase Slip and Flux quantization
The Single Cooper Pair Josephson Transistor is a device that exhibits at the
same time charge quantization and phase coherence. Coherent quantum phase slip
phenomenon is "dual" the Josephson phase coherence while the charge
quantization is dual to the flux quantization. We present the experimental
demonstration and the theoretical description of a new superconducting device -
Single Flux Transistor, which is dual to the Single Cooper Pair Transistor. Our
transport measurements show the periodic modulation of the critical voltage by
the external magnetic field. The obtained current-voltage characteristics show
the hysteretic behavior, which we attribute to the intrinsic self-heating of
charge carriers.Comment: 5 pages, 4 figure
Parity effect and single-electron injection for Josephson-junction chains deep in the insulating state
We have made a systematic investigation of charge transport in 1D chains of
Josephson junctions where the characteristic Josephson energy is much less than
the single-island Cooper-pair charging energy, . Such
chains are deep in the insulating state, where superconducting phase coherence
across the chain is absent, and a voltage threshold for conduction is observed
at the lowest temperatures. We find that Cooper-pair tunneling in such chains
is completely suppressed. Instead, charge transport is dominated by tunneling
of single electrons, which is very sensitive to the presence of BCS
quasiparticles on the superconducting islands of the chain. Consequently we
observe a strong parity effect, where the threshold voltage vanishes sharply at
a characteristic parity temperature , which is significantly lower than
the the critical temperature, . A measurable and thermally-activated
zero-bias conductance appears above , with an activation energy equal to
the superconducting gap, confirming the role of thermally-excited
quasiparticles. Conduction below and above the voltage threshold occurs
via injection of single electrons/holes into the Cooper-pair insulator, forming
a non-equilibrium steady state with a significantly enhanced effective
temperature. Our results explicitly show that single-electron transport
dominates deep in the insulating state of Josephson-junction arrays. This
conduction process has mostly been ignored in previous studies of both
superconducting junction arrays and granular superconducting films below the
superconductor-insulator quantum phase transition.Comment: 8 pages, 6 figure
Pumping properties of the hybrid single-electron transistor in dissipative environment
Pumping characteristics were studied of the hybrid
normal-metal/superconductor single-electron transistor embedded in a high-ohmic
environment. Two 3 micrometer-long microstrip resistors of CrOx with a sum
resistance R=80kOhm were placed adjacent to this hybrid device. Substantial
improvement of pumping and reduction of the subgap leakage were observed in the
low-MHz range. At higher frequencies 0.1-1GHz, a slowdown of tunneling due to
the enhanced damping and electron heating negatively affected the pumping, as
compared to the reference bare devices.Comment: 3 pages 4 figure
Measurement of the shot noise in a single electron transistor
We have systematically measured the shot noise in a single electron
transistor (SET) as a function of bias and gate voltages. By embedding a SET in
a resonance circuit we have been able to measure its shot noise at the
resonance frequency 464 MHz, where the 1/f noise is negligible. We can extract
the Fano factor which varies between 0.5 and 1 depending on the amount of
Coulomb blockade in the SET, in very good agreement with the theory.Comment: 4 figure
Charge noise in single-electron transistors and charge qubits may be caused by metallic grains
We report on measurements of low-frequency noise in a single-electron transistor (SET) from a few hertz up to 10 MHz. Measurements were done for different bias and gate voltages, which allow us to separate noise contributions from different noise sources. We find a 1/f noise spectrum with two Lorentzians superimposed. The cut-off frequency of one of the Lorentzians varies systematically with the potential of the SET island. Our data is consistent with two single-charge fluctuators situated close to the tunnel barrier. We suggest that these are due to random charging of aluminum grains, each acting as a single-electron box with tunnel coupling to one of the leads and capacitively coupled to the SET island. We are able to fit the data to our model and extract parameters for the fluctuators
A planar Al-Si Schottky Barrier MOSFET operated at cryogenic temperatures
Schottky Barrier (SB)-MOSFET technology offers intriguing possibilities for
cryogenic nano-scale devices, such as Si quantum devices and superconducting
devices. We present experimental results on a novel device architecture where
the gate electrode is self-aligned with the device channel and overlaps the
source and drain electrodes. This facilitates a sub-5 nm gap between the
source/drain and channel, and no spacers are required. At cryogenic
temperatures, such devices function as p-MOS Tunnel FETs, as determined by the
Schottky barrier at the Al-Si interface, and as a further advantage,
fabrication processes are compatible with both CMOS and superconducting logic
technology.Comment: 6 pages, 4 figures, minor changes from the previous version
Photon assisted tunneling as an origin of the Dynes density of states
We show that the effect of a high-temperature environment in current
transport through a normal metal-insulator-superconductor tunnel junction can
be described by an effective density of states (DOS) in the superconductor. In
the limit of a resistive low-ohmic environment, this DOS reduces into the
well-known Dynes form. Our theoretical result is supported by experiments in
engineered environments. We apply our findings to improve the performance of a
single-electron turnstile, a potential candidate for a metrological current
source.Comment: 4+3 pages, 4 figures; updated to the published version, includes
EPAPS supplementary materia
Experimental investigation of hybrid single-electron turnstiles with high charging energy
We present an experimental study of hybrid turnstiles with high charging
energies in comparison to the superconducting gap. The device is modeled with
the sequential tunneling approximation. The backtunneling effect is shown to
limit the amplitude of the gate drive and thereby the maximum pumped current of
the turnstile. We compare results obtained with sine and square wave drive and
show how a fast rise time can suppress errors due to leakage current. Quantized
current plateaus up to 160 pA are demonstrated.Comment: 4 pages, 3 figure
Parallel pumping of electrons
We present simultaneous operation of ten single-electron turnstiles leading
to one order of magnitude increase in current level up to 100 pA. Our analysis
of device uniformity and background charge stability implies that the
parallelization can be made without compromising the strict requirements of
accuracy and current level set by quantum metrology. In addition, we discuss
how offset charge instability limits the integration scale of single-electron
turnstiles.Comment: 6 pages, 4 figures, 1 tabl
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