2,338 research outputs found
Effect of Measurement on the Periodicity of the Coulomb Staircase of a Superconducting Box
We report on the effect of the back-action of a Single Cooper Pair Transistor
electrometer (E) on the measurement of charge on the island of a
superconducting box (B). The charge is e-periodic in the gate bias of B when E
is operated near voltages 2Delta/e or 4Delta/e. We show that this is due to
quasiparticle poisoning of B at a rate proportional to the number of
quasiparticle tunneling events in E per second. We are able to eliminate this
back action and recover 2e charge periodicity using a new measurement method
based on switching current modulation of E.Comment: 4 pages, 4 figures, revised versio
Observation of Strong Coulomb Blockade in Resistively Isolated Tunnel Junctions
We report measurements of the Coulomb-blockade current in resistively
isolated (R_{Isol} >> h/e^{2}) tunnel junctions for the temperature range 60mK
R_{Isol}\gg h/e^{2})$ tunnel junctions for the temperature range 60mK < T <
230mK where the charging energy E_{c} is much greater than the thermal energy.
A zero-bias resistance R_{0} of up to 10^{4}R_{T} (the tunnel resistance of the
bare junction) is obtained. For eV << E_{c}, the I-V curves for a given
R_{Isol} scale as a function of V/T, with I \propto V^{\alpha (R_{Isol})} over
a range of V. The data agree well with numerical calculations of the tunneling
rate that include environmental effects.Comment: 13 pages, 3 eps figure
Radiation Due to Josephson Oscillations in Layered Superconductors
We derive the power of direct radiation into free space induced by Josephson
oscillations in intrinsic Josephson junctions of highly anisotropic layered
superconductors. We consider the super-radiation regime for a crystal cut in
the form of a thin slice parallel to the c-axis. We find that the radiation
correction to the current-voltage characteristic in this regime depends only on
crystal shape. We show that at large enough number of junctions oscillations
are synchronized providing high radiation power and efficiency in the THz
frequency range. We discuss crystal parameters and bias current optimal for
radiation power and crystal cooling.Comment: 4 pages, 1 figure, to be published in Phys. Rev. Let
Crossover from Kramers to phase-diffusion switching in hysteretic DC-SQUIDs
We have measured and propose a model for switching rates in hysteretic
DC-SQUID in the regime where phase diffusion processes start to occur. We show
that the switching rates in this regime are smaller than the rates given by
Kramers' formula due to retrapping of Josephson phase. The retrapping process,
which is affected by the frequency dependent impedance of the environment of
the DC-SQUID, leads to a peaked second moment of the switching distribution as
a function of temperature. The temperature where the peaks occur are
proportional to the critical current of the DC- SQUID.Comment: 4 pages, 4 figure
Flux amplification using stochastic superconducting quantum interference devices
This is the published version, also available here: http://dx.doi.org/10.1063/1.114161.The flux change δ Φ through a bistable superconducting quantum interference device has been measured in the presence of thermally induced switching (with rate Γ) versus δ Φ x , the change in the applied flux. For small δ Φ x , δ Φ is proportional to δ Φ x with a measured flux gain g, depending on the temperature, barrier height, and frequency Ω, with a maximum of about 16. In agreement with theories of periodically driven stochastic bistable systems,g(Ω) is nearly frequency independent up to Γ and is proportional to Ω−1 for Ω≫Γ. For larger amplitude signals, harmonic generation has been measured in the adiabatic limit (Ω≪Γ) and found to be in good agreement with theory. Possible applications of this system for flux measurement are discussed
The imprint of strong-storm tracks on winter weather in North America
Northern Hemisphere winter storm tracks and their relation to winter weather are investigated using CFSR data. Storm tracks are described by isentropic PV maxima within a Lagrangian framework; these correspond well with those described in previous studies. Our diagnostics focus on strong-storm tracks, which are comprised of storms that achieve a maximum PV exceeding the mean value by one standard deviation. Large increases in diabatic heating related to deep convection occur where the storm tracks are most intense. The cyclogenesis pattern shows that strong storms generally develop on the upstream sectors of the tracks. Intensification happens towards the eastern North Pacific and all across the North Atlantic Ocean, where enhanced storm track-related weather is found.
In this study, the relation of storm tracks to near-surface winds and precipitation is evaluated. The largest increases in storm track-related winds are found where strong storms tend to develop and intensify, while storm precipitation is enhanced in areas where the storm tracks have the highest intensity. Strong storms represent about 16% of all storms but contribute 30-50% of the storm precipitation in the storm track regions. Both strong-storm related winds and precipitation are prone to cause storm-related losses in the eastern US and North American coasts. Over the oceans, maritime operations are expected to be most vulnerable to damage offshore of the US coasts. Despite making up a small fraction of all storms, the strong-storm tracks have a significant imprint on winter weather in North America potentially leading to structural and economic loss
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