84 research outputs found
Collapse of thermal activation in moderately damped Josephson junctions
We study switching current statistics in different moderately damped
Josephson junctions: a paradoxical collapse of the thermal activation with
increasing temperature is reported and explained by interplay of two
conflicting consequences of thermal fluctuations, which can both assist in
premature escape and help in retrapping back into the stationary state. We
analyze the influence of dissipation on the thermal escape by tuning the
damping parameter with a gate voltage, magnetic field, temperature and an
in-situ capacitor.Comment: 4 pages, 4 figure
Spectroscopy of SrRuO/Ru Junctions in Eutectic
We have investigated the tunnelling properties of the interface between
superconducting Sr2RuO4 and a single Ru inclusion in eutectic. By using a
micro-fabrication technique, we have made Sr2RuO4/Ru junctions on the eutectic
system that consists of Sr2RuO4 and Ru micro-inclusions. Such a eutectic system
exhibits surface superconductivity, called the 3-K phase. A zero bias
conductance peak (ZBCP) was observed in the 3-K phase. We propose to use the
onset of the ZBCP to delineate the phase boundary of a time-reversal symmetry
breaking state.Comment: To be published in Proc of 24th Int. Conf. on Low Temperature Physics
(LT24); 2 page
A Cooper pair light emitting diode
We demonstrate Cooper-pair's drastic enhancement effect on band-to-band
radiative recombination in a semiconductor. Electron Cooper pairs injected from
a superconducting electrode into an active layer by the proximity effect
recombine with holes injected from a p-type electrode and dramatically
accelerate the photon generation rates of a light emitting diode in the
optical-fiber communication band. Cooper pairs are the condensation of
electrons at a spin-singlet quantum state and this condensation leads to the
observed enhancement of the electric-dipole transitions. Our results indicate
the possibility to open up new interdisciplinary fields between
superconductivity and optoelectronics.Comment: 5 pages (4 figures
Interface-aware signal temporal logic
Safety and security are major concerns in the development of Cyber-Physical Systems (CPS). Signal temporal logic (STL) was proposedas a language to specify and monitor the correctness of CPS relativeto formalized requirements. Incorporating STL into a developmentprocess enables designers to automatically monitor and diagnosetraces, compute robustness estimates based on requirements, andperform requirement falsification, leading to productivity gains inverification and validation activities; however, in its current formSTL is agnostic to the input/output classification of signals, andthis negatively impacts the relevance of the analysis results.In this paper we propose to make the interface explicit in theSTL language by introducing input/output signal declarations. Wethen define new measures of input vacuity and output robustnessthat better reflect the nature of the system and the specification in-tent. The resulting framework, which we call interface-aware signaltemporal logic (IA-STL), aids verification and validation activities.We demonstrate the benefits of IA-STL on several CPS analysisactivities: (1) robustness-driven sensitivity analysis, (2) falsificationand (3) fault localization. We describe an implementation of our en-hancement to STL and associated notions of robustness and vacuityin a prototype extension of Breach, a MATLAB®/Simulink®toolboxfor CPS verification and validation. We explore these methodologi-cal improvements and evaluate our results on two examples fromthe automotive domain: a benchmark powertrain control systemand a hydrogen fuel cell system
Photoluminescence fine structures in the fractional quantum Hall effect regime
We investigate polarization-resolved fine structure in the photoluminescence (PL) in the fractional quantum Hall effect regime at B=4–6 T, where small Zeeman energy allows spin-depolarized ground states. We observe up to five distinct peaks with characteristic polarization and temperature dependence in the vicinity of ν=1/3 and quenching of the PL from triplet charged quasiexcitons at around ν=1/4. Those findings appear to be consistent with results of exact diagonalization on a Haldane sphere including all spin configurations and are understood to be PL from fractionally charged quasiexcitons
A superconducting-nanowire 3-terminal electronic device
In existing superconducting electronic systems, Josephson junctions play a
central role in processing and transmitting small-amplitude electrical signals.
However, Josephson-junction-based devices have a number of limitations
including: (1) sensitivity to magnetic fields, (2) limited gain, (3) inability
to drive large impedances, and (4) difficulty in controlling the junction
critical current (which depends sensitively on sub-Angstrom-scale thickness
variation of the tunneling barrier). Here we present a nanowire-based
superconducting electronic device, which we call the nanocryotron (nTron), that
does not rely on Josephson junctions and can be patterned from a single thin
film of superconducting material with conventional electron-beam lithography.
The nTron is a 3-terminal, T-shaped planar device with a gain of ~20 that is
capable of driving impedances of more than 100 k{\Omega}, and operates in
typical ambient magnetic fields at temperatures of 4.2K. The device uses a
localized, Joule-heated hotspot formed in the gate to modulate current flow in
a perpendicular superconducting channel. We have characterized the nTron,
matched it to a theoretical framework, and applied it both as a digital logic
element in a half-adder circuit, and as a digital amplifier for superconducting
nanowire single-photon detectors pulses. The nTron has immediate applications
in classical and quantum communications, photon sensing and astronomy, and its
performance characteristics make it compatible with existing superconducting
technologies. Furthermore, because the hotspot effect occurs in all known
superconductors, we expect the design to be extensible to other materials,
providing a path to digital logic, switching, and amplification in
high-temperature superconductors
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