113 research outputs found
Properties of small HTSC mesa structures: common problems of interlayer tunneling
I analyze common problems of interlayer tunneling in Bi-2212 mesa structures,
such as self-heating and nonuniformity of junctions. Numerical simulations have
shown that self-heating does not mask the temperature dependence of the
superconducting gap. Major problems can be avoided by decreasing mesa sizes.Comment: 3 pages, 4 figures, presentation at EUCAS-2001 (Copenhagen, August
2001) Subm. to Physica
Stacked Josephson junction SQUID
Operation of a Superconducting Quantum Interference Device (SQUID) made of
stacked Josephson junctions is analyzed numerically for a variety of junction
parameters. Due to a magnetic coupling of junctions in the stack, such a SQUID
has certain advantages as compared to an uncoupled multi-junction SQUID.
Namely, metastability of current-flux modulation can be reduced and a
voltage-flux modulation can be improved if junctions in the stack are
phase-locked. Optimum operation of the SQUID is expected for moderately long,
strongly coupled stacked Josephson junctions. A possibility of making a stacked
Josephson junction SQUID based on intrinsic Josephson junctions in high-Tc
superconductor is discussed.Comment: 4 pages, 3 figures, presented at SQUID-2001 (Stenungsbaden September
2001
In-plane fluxon in layered superconductors with arbitrary number of layers
I derive an approximate analytic solution for the in-plane vortex (fluxon) in
layered superconductors and stacked Josephson junctions (SJJ's) with arbitrary
number of layers. The validity of the solution is verified by numerical
simulation. It is shown that in SJJ's with large number of thin layers,
phase/current and magnetic field of the fluxon are decoupled from each other.
The variation of phase/current is confined within the Josephson penetration
depth, , along the layers, while magnetic field decays at the
effective London penetration depth, . For comparison
with real high- superconducting samples, large scale numerical simulations
with up to 600 SJJ's and with in-plane length up to 4000 %, are
presented. It is shown, that the most striking feature of the fluxon is a
Josephson core, manifesting itself as a sharp peak in magnetic induction at the
fluxon center.Comment: 4 pages, 4 figures. Was presented in part at the First Euroconference
on Vortex Matter in Superconductors (Crete, September 1999
The shape of a moving fluxon in stacked Josephson junctions
We study numerically and analytically the shape of a single fluxon moving in
a double stacked Josephson junctions (SJJ's) for various junction parameters.
We show that the fluxon in a double SJJ's consists of two components, which are
characterized by different Swihart velocities and Josephson penetration depths.
The weight coefficients of the two components depend on the parameters of the
junctions and the velocity of the fluxon. It is shown that the fluxon in SJJ's
may have an unusual shape with an inverted magnetic field in the second
junction when the velocity of the fluxon is approaching the lower Swihart
velocity. Finally, we study the influence of fluxon shape on flux-flow
current-voltage characteristics and analyze the spectrum of Cherenkov radiation
for fluxon velocity above the lower Swihart velocity. Analytic expression for
the wavelength of Cherenkov radiation is derived.Comment: 12 pages, 12 figure
Intrinsic tunneling spectroscopy: A look from the inside at HTSC
Layered structure of Bi-2212 high superconductor (HTSC), provides a
unique opportunity to probe quasiparticle density of states inside a bulk
single crystal by means of intrinsic (interlayer) tunneling spectroscopy. Here
I present a systematic study of intrinsic tunneling characteristics of Bi-2212
as a function of doping, temperature, magnetic field and intercalation. An
improved resolution made it possible to simultaneously trace the
superconducting gap (SG) and the normal state pseudo-gap (PG) in a close
vicinity of and to analyze closing of the PG at . The obtained
doping phase diagram exhibits a critical doping point for appearance of the PG
and a characteristic crossing of the SG and the PG close to the optimal doping.
All this points towards coexistence of two different and competing order
parameters in Bi-2212.Comment: 4 pages, 5 figures, Presentation at M2S-Rio (May 2003), Subm. to
Physica C. Note: A discussion of magnetic field dependencies is adde
Interlayer tunneling spectroscopy of BiSrCaCuO: a look from inside on the doping phase diagram of high superconductors
A systematic, doping dependent interlayer tunneling spectroscopy of Bi2212
high superconductor is presented. An improved resolution made it possible
to simultaneously trace the superconducting gap (SG) and the normal state
pseudo-gap (PG) in a close vicinity of and to analyze closing of the PG
at . The obtained doping phase diagram exhibits a critical doping point
for appearance of the PG and a characteristic crossing of the SG and the PG
close to the optimal doping. This points towards coexistence of two different
and competing order parameters in Bi2212. Experimental data indicate that the
SG can form a combined (large) gap with the PG at and that the
interlayer tunneling becomes progressively incoherent with decreasing doping.Comment: 5 pages, 5 figure
Single fluxon in double stacked Josephson junctions: Analytic solution
We derive an approximate analytic solution for a single fluxon in a double
stacked Josephson junctions (SJJ's) for arbitrary junction parameters and
coupling strengths. It is shown that the fluxon in a double SJJ's can be
characterized by two components, with different Swihart velocities and
Josephson penetration depths. Using the perturbation theory we find the second
order correction to the solution and analyze its accuracy. Comparison with
direct numerical simulations shows a quantitative agreement between exact and
approximate analytic solutions. It is shown that due to the presence of two
components, the fluxon in SJJ's may have an unusual shape with an inverted
magnetic field in the second junction when the velocity of the fluxon is
approaching the lower Swihart velocity.Comment: 4 pages, 3 figure
Magnetic field dependence of the critical current in stacked Josephson junctions. Evidence for fluxon modes in Bi2Sr2CaCu2O8+x mesas
Modulation of the critical current across layers, Ic(H), of stacked Josephson
junctions (SJJs) as a function of an applied magnetic field parallel to the
junction planes is studied theoretically and experimentally for different
junction lengths and coupling parameters. It is shown that the Ic(H) patterns
of long SJJs are very complicated without periodicity in H. This is due to
interaction between junctions in the stack. This, in turn, gives rise to the
existence of multiple quasi-equilibrium Josephson fluxon modes and submodes
which are different with respect to the symmetry of the phase and the fluxon
sequence in SJJs. The critical current of long SJJs is multiple valued and is
governed by switching between energetically close fluxon modes/submodes. Due to
this, the probability distribution of the critical current may become wide and
may consist of multiple maxima each representing a particular mode/submode.
Experimentally, multiple branched Ic(H) patterns and multiple maxima in the Ic
probability distribution were observed for Bi2Sr2CaCu2O8+x intrinsic SJJs,
which are in a good agreement with numerical simulations and support the idea
of having different quasi-equilibrium fluxon modes/submodes in intrinsic SJJs.Comment: 5 pages, 5 figure
Planar SFS Josephson Junctions Made by Focused Ion Beam Etching
Superconductor-Ferromagnet-Superconductor (S-F-S) Josephson junctions were
fabricated by making a narrow cut through a S-F double layer using direct
writing by Focused Ion Beam (FIB). Due to a high resolution (spot size smaller
than 10 nm) of FIB, junctions with a small separation between superconducting
electrodes ( 30 nm) can be made. Such a short distance is sufficient for
achieving a considerable proximity coupling through a diluted CuNi ferromagnet.
We have successfully fabricated and studied S-F-S (Nb-CuNi-Nb) and S-S'-S
(Nb-Nb/CuNi-Nb) junctions. Junctions exhibit clear Fraunhofer modulation of the
critical current as a function of magnetic field, indicating good uniformity of
the cut. By changing the depth of the cut, junctions with the product
ranging from 0.5 mV to V were fabricated.Comment: 5 pages, 5 figures, presentation at EUCAS-2003, to be published in
Physica
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