2,037 research outputs found
Production of non-local quartets and phase-sensitive entanglement in a superconducting beam splitter
Three BCS superconductors S_a, S_b, and S and two short normal regions N_a
and N_b in a three-terminal S_aN_aSN_bS_b set-up provide a source of non-local
quartets spatially separated as two correlated pairs in S_a and S_b, if the
distance between the interfaces N_aS and SN_b is comparable to the coherence
length in S. Low-temperature dc-transport of non-local quartets from S to S_a
and S_b can occur in equilibrium, and also if S_a and S_b are biased at
opposite voltages. At higher temperatures, thermal excitations result in
correlated current fluctuations which depend on the superconducting phases
phi_a and phi_b in S_a and S_b. Phase-sensitive entanglement is obtained at
zero temperature if N_a and N_b are replaced by discrete levels.Comment: 4 pages, 2 figures; technical details attached in ancillary file
http://arxiv.org/src/1102.2355v4/anc/EPAPS_Freyn_2011.pdf; higher versions:
minor corrections, cleanup and corrected reference
Electrical stress effect on Josephson tunneling through ultrathin AlOx barrier in Nb/Al/AlOx/Nb junctions
The effect of dc electrical stress and breakdown on Josephson and
quasiparticle tunneling in Nb/Al/AlOx/Nb junctions with ultrathin AlOx barriers
typical for applications in superconductor digital electronics has been
investigated. The junctions' conductance at room temperature and
current-voltage (I-V) characteristics at 4.2 K have been measured after the
consecutive stressing of the tunnel barrier at room temperature. Electrical
stress was applied using current ramps with increasing amplitude ranging from 0
to ~1000 Ic corresponding to voltages across the barrier up to 0.65 V where Ic
is the Josephson critical current. A very soft breakdown has been observed with
polarity-dependent breakdown current (voltage). A dramatic increase in subgap
conductance of the junctions, the appearance of subharmonic current steps, and
gradual increase in both the critical and the excess currents as well as a
decrease in the normal-state resistance have been observed. The observed
changes in superconducting tunneling suggest a model in which a progressively
increasing number of defects and associated additional conduction channels
(superconducting quantum point contacts (SQPCs)) are induced by electric field
in the tunnel barrier. By comparing the I-V characteristics of these conduction
channels with the nonstationary theory of current transport in SQPCs based on
multiple Andreev reflections by Averin and Bardas, the typical transparency D
of the induced SQPCs was estimated as D ~ 0.7. The number of induced SQPCs was
found to grow with voltage across the barrier as sinh(V/V_0) with V_0 = 0.045
V, in good agreement with the proposed model of defect formation by ion
electromigration. The observed polarity dependence of the breakdown current
(voltage) is also consistent with the model.Comment: 11 pages, 10 figure
Interactions and Interference in Quantum Dots: Kinks in Coulomb Blockade Peak Positions
We investigate the spin of the ground state of a geometrically confined
many-electron system. For atoms, shell structure simplifies this problem-- the
spin is prescribed by the well-known Hund's rule. In contrast, quantum dots
provide a controllable setting for studying the interplay of quantum
interference and electron-electron interactions in general cases. In a generic
confining potential, the shell-structure argument suggests a singlet ground
state for an even number of electrons. The interaction among the electrons
produces, however, accidental occurrences of spin-triplet ground states, even
for weak interaction, a limit which we analyze explicitly. Variaton of an
external parameter causes sudden switching between these states and hence a
kink in the conductance. Experimental study of these kinks would yield the
exchange energy for the ``chaotic electron gas''.Comment: 4 pages, 2 ps figs included using epsf.sty. Revision: added important
reference and consequent text changes, other small correction
Exudative pericarditis with tamponade after COVID-19. Case report
A description of a COVID-19 patient with the development of exudative pericarditis complicated by cardiac tamponade is provid. A peculiarity of this case is the presence of an underlying disease in the patient (chronic lymphocytic leukemia), which was in remission for 1.5 years after chemotherapy. Another feature of the patient was the relatively small area of lung damage and the hemorrhagic nature of the pericardial effusion, which persisted for a long time. The insignificant activity of inflammatory markers was noteworthy. Possible mechanisms of development and features of the course of exudative pericarditis in the described patient, issues of diagnosis and treatment of this category of patients are discusse
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