214 research outputs found
Superconducting MoSi nanowires
We have fabricated disordered superconducting nanowires of molybdenium
silicide. A molybdenium nanowire is first deposited on top of silicon, and the
alloy is formed by rapid thermal annealing. The method allows tuning of the
crystal growth to optimise, e.g., the resistivity of the alloy for potential
applications in quantum phase slip devices and superconducting nanowire
single-photon detectors. The wires have effective diameters from 42 to 79 nm,
enabling the observation of crossover from conventional superconductivity to
regimes affected by thermal and quantum fluctuations. In the smallest diameter
wire and at temperatures well below the superconducting critical temperature,
we observe residual resistance and negative magnetoresistance, which can be
considered as fingerprints of quantum phase slips
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
Long hold times in a two-junction electron trap
The hold time of a single-electron trap is shown to increase
significantly due to suppression of environmentally assisted tunneling events.
Using two rf-tight radiation shields instead of a single one, we demonstrate
increase of by a factor exceeding , up to about 10 hours, for a
trap with only two superconductor (S) -- normal-metal (N) tunnel junctions and
an on-chip resistor (R-SNS structure). In the normal state, the improved
shielding made it possible to observe 100 s, which is in reasonable
agreement with the quantum-leakage-limited level expected for the two-electron
cotunneling process.Comment: 4 pages, 3 figure
Single-electron current sources: towards a refined definition of ampere
Controlling electrons at the level of elementary charge has been
demonstrated experimentally already in the 1980's. Ever since, producing an
electrical current , or its integer multiple, at a drive frequency has
been in a focus of research for metrological purposes. In this review we first
discuss the generic physical phenomena and technical constraints that influence
charge transport. We then present the broad variety of proposed realizations.
Some of them have already proven experimentally to nearly fulfill the demanding
needs, in terms of transfer errors and transfer rate, of quantum metrology of
electrical quantities, whereas some others are currently "just" wild ideas,
still often potentially competitive if technical constraints can be lifted. We
also discuss the important issues of read-out of single-electron events and
potential error correction schemes based on them. Finally, we give an account
of the status of single-electron current sources in the bigger framework of
electric quantum standards and of the future international SI system of units,
and briefly discuss the applications and uses of single-electron devices
outside the metrological context.Comment: 55 pages, 38 figures; (v2) fixed typos and misformatted references,
reworded the section on AC pump
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
Understanding Teacher Evaluation in Finland: A Professional Development Framework
This study explores the characteristics of the teacher evaluation model in Finland. Highlighting the unique qualities of the Finnish case, we also compare these teacher evaluation practices with the increasingly applied value-added model (VAM) for teacher evaluation across the globe. Our analysis revealed that the Finnish Model prioritises teacher empowerment and professional development by carrying out bottom-up evaluation practices. With a clear focus on teacher empowerment and professional development, this framework substantially differs from accountability measures such as VAM, which emphasize rigid data collection procedures and the use of standardized test scores to hold teachers accountable based on their students’ academic performance. This study also revealed that professional development endeavours of teachers are highlighted as the key elements in Finnish teacher evaluation. Ongoing needs analyses for professional development also form the basis for assessing teachers in Finland
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
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
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