57 research outputs found
Microscopic model for multiple flux transitions in mesoscopic superconducting loops
A microscopic model is constructed which is able to describe multiple
magnetic flux transitions as observed in recent ultra-low temperature tunnel
experiments on an aluminum superconducting ring with normal metal - insulator -
superconductor junctions [Phys. Rev. B \textbf{70}, 064514 (2004)]. The unusual
multiple flux quantum transitions are explained by the formation of metastable
states with large vorticity. Essential in our description is the modification
of the pairing potential and the superconducting density of states by a
sub-critical value of the persistent current which modulates the measured
tunnel current. We also speculate on the importance of the injected
non-equilibrium quasiparticles on the stability of these metastable states.Comment: 6 pages, 3 figure
Negative magnetoresistance and phase slip process in superconducting nanowires
We argue that the negative magnetoresistance of superconducting nanowires,
which was observed in recent experiments, can be explained by the influence of
the external magnetic field on the critical current of the phase slip process.
We show that the suppression of the order parameter in the bulk superconductors
made by an external magnetic field can lead to an enhancement of both the first
and the second critical currents of the phase slip process in
nanowires. Another mechanism of an enhancement of can come from
decreasing the decay length of the charge imbalance at weak
magnetic fields because is inversely proportional to . The
enhancement of the first critical current leads to a larger intrinsic
dissipation of the phase slip process. It suppresses the rate of both the
thermo-activated and/or quantum fluctuated phase slips and results in
decreasing the fluctuated resistance.Comment: 7 pages, 4 figure
Enhancement of superconductivity in NbN nanowires by negative electron-beam lithography with positive resist
We performed comparative experimental investigation of superconducting NbN
nanowires which were prepared by means of positive-and negative electron-beam
lithography with the same positive tone Poly-methyl-methacrylate (PMMA) resist.
We show that nanowires with a thickness 4.9 nm and widths less than 100 nm
demonstrate at 4.2 K higher critical temperature and higher density of critical
and retrapping currents when they are prepared by negative lithography. Also
the ratio of the experimental critical-current to the depairing critical
current is larger for nanowires prepared by negative lithography. We associate
the observed enhancement of superconducting properties with the difference in
the degree of damage that nanowire edges sustain in the lithographic process. A
whole range of advantages which is offered by the negative lithography with
positive PMMA resist ensures high potential of this technology for improving
performance metrics of superconducting nanowire singe-photon detectors
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