385 research outputs found
Whole-brain patterns of 1H-magnetic resonance spectroscopy imaging in Alzheimer's disease and dementia with Lewy bodies
Acknowledgements We thank Craig Lambert for his help in processing the MRS data. The study was funded by the Sir Jules Thorn Charitable Trust (grant ref: 05/JTA) and was supported by the National Institute for Health Research (NIHR) Newcastle Biomedical Research Centre and the Biomedical Research Unit in Lewy Body Dementia based at Newcastle upon Tyne Hospitals National Health Service (NHS) Foundation Trust and Newcastle University and the NIHR Biomedical Research Centre and Biomedical Research Unit in Dementia based at Cambridge University Hospitals NHS Foundation Trust and the University of Cambridge.Peer reviewedPublisher PD
Depairing critical current achieved in superconducting thin films with through-thickness arrays of artificial pinning centers
Large area arrays of through-thickness nanoscale pores have been milled into
superconducting Nb thin films via a process utilizing anodized aluminum oxide
thin film templates. These pores act as artificial flux pinning centers,
increasing the superconducting critical current, Jc, of the Nb films. By
optimizing the process conditions including anodization time, pore size and
milling time, Jc values approaching and in some cases matching the
Ginzburg-Landau depairing current of 30 MA/cm^2 at 5 K have been achieved - a
Jc enhancement over as-deposited films of more than 50 times. In the field
dependence of Jc, a matching field corresponding to the areal pore density has
also been clearly observed. The effect of back-filling the pores with magnetic
material has then been investigated. While back-filling with Co has been
successfully achieved, the effect of the magnetic material on Jc has been found
to be largely detrimental compared to voids, although a distinct influence of
the magnetic material in producing a hysteretic Jc versus applied field
behavior has been observed. This behavior has been tested for compatibility
with currently proposed models of magnetic pinning and found to be most closely
explained by a model describing the magnetic attraction between the flux
vortices and the magnetic inclusions.Comment: 9 pages, 10 figure
Characteristics of strong ferromagnetic Josephson junctions with epitaxial barriers
We present the measurement of superconductor/ferromagnetic Josephson junctions, based on an epitaxial Nb bottom electrode and epitaxial Fe20Ni80 barrier. Uniform junctions have been fabricated with a barrier thicknesses in the range 2-12 nm. The maximum critical current density similar to 2.4 +/- 0.2 x 10(9) Am-2 was found for a device with a 3-nm-thick barrier at 4.2 K, corresponding to an average characteristic voltage ICRN similar to 16 mu V. The ICRN showed a nonmonotonic behavior with Fe20Ni80 thickness. The variation of the resistance of a unit area AR(N), of the junctions with barrier thickness gave a Nb/Py specific interface resistance of 6.0 +/- 0.5 f Omega m(2) and Fe20Ni80 resistivity of 174 +/- 50 n Omega m, consistent with other studies in polycrystalline samples
Josephson effects in MgB2 meta masked ion damage junctions
Ion beam damage combined with nanoscale focused ion beam direct milling was
used to create manufacturable SNS type Josephson junctions in 100 nm thick
MgB with T of 38 K. The junctions show non-hysteretic current -
voltage characteristics between 36 and 4.2 K. Experimental evidence for the dc
and ac Josephson effects in MgB metal masked ion damage junctions are
presented. This technique is particularly useful for prototyping devices due to
its simplicity and flexibility of fabrication and has a great potential for
high-density integration.Comment: 12 pages, 4 figures, RevTeX4, submitted to AP
Electrodynamics of Josephson junctions containing strong ferromagnets
Triplet supercurrents in multilayer ferromagnetic Josephson junctions with
misaligned magnetization can penetrate thicker ferromagnetic barriers compared
to the singlet component. Although the static properties of these junctions
have been extensively studied, the dynamic characteristics remain largely
unexplored. Here we report a comprehensive electrodynamic characterization of
multilayer ferromagnetic Josephson junctions composed of Co and Ho. By
measuring the temperature-dependent current-voltage characteristics and the
switching current distributions down to 0.3 K, we show that phase dynamics of
junctions with triplet supercurrents exhibits long (in terms of proximity)
junction behavior and moderately damped dynamics with renormalized capacitance
and resistance. This unconventional behavior possibly provides a different way
to dynamically detect triplets. Our results show new theoretical models are
required to fully understand the phase dynamics of triplet Josephson junctions
for applications in superconducting spintronics.DM, RC, FT would like to thank NANOCOHYBRI project (Cost Action CA 16218). NB acknowledges funding from the British Council through UKIERI programme and Loughborough University. MGB acknowledges funding from EPSRC Programme Grant EP/N017242/1
Supra-oscillatory critical temperature dependence of Nb-Ho bilayers
We investigate the critical temperature Tc of a thin s-wave superconductor
(Nb) proximity coupled to a helical rare earth ferromagnet (Ho). As a function
of the Ho layer thickness, we observe multiple oscillations of Tc superimposed
on a slow decay, that we attribute to the influence of the Ho on the Nb
proximity effect. Because of Ho inhomogeneous magnetization, singlet and
triplet pair correlations are present in the bilayers. We take both into
consideration when solving the self consistent Bogoliubov-de Gennes equations,
and we observe a reasonable agreement. We also observe non-trivial transitions
into the superconducting state, the zero resistance state being attained after
two successive transitions which appear to be associated with the magnetic
structure of Ho.Comment: Main article: 5 pages, 4 figures; Supplementary materials: 4 pages, 5
figure
Vortex deformation and breaking in superconductors: A microscopic description
Vortex breaking has been traditionally studied for nonuniform critical
current densities, although it may also appear due to nonuniform pinning force
distributions. In this article we study the case of a
high-pinning/low-pinning/high-pinning layered structure. We have developed an
elastic model for describing the deformation of a vortex in these systems in
the presence of a uniform transport current density for any arbitrary
orientation of the transport current and the magnetic field. If is above a
certain critical value, , the vortex breaks and a finite effective
resistance appears. Our model can be applied to some experimental
configurations where vortex breaking naturally exists. This is the case for
YBaCuO (YBCO) low angle grain boundaries and films on vicinal
substrates, where the breaking is experienced by Abrikosov-Josephson vortices
(AJV) and Josephson string vortices (SV), respectively. With our model, we have
experimentally extracted some intrinsic parameters of the AJV and SV, such as
the line tension and compared it to existing predictions based on
the vortex structure.Comment: 11 figures in 13 files; minor changes after printing proof
Tuning of Magnetic Activity in Spin-Filter Josephson Junctions Towards Spin-Triplet Transport.
The study of superconductor-ferromagnet interfaces has generated great interest in the last decades, leading to the observation of spin-aligned triplet supercurrents and 0-Ï transitions in Josephson junctions where two superconductors are separated by an itinerant ferromagnet. Recently, spin-filter Josephson junctions with ferromagnetic barriers have shown unique transport properties, when compared to standard metallic ferromagnetic junctions, due to the intrinsically nondissipative nature of the tunneling process. Here we present the first extensive characterization of spin polarized Josephson junctions down to 0.3Â K, and the first evidence of an incomplete 0-Ï transition in highly spin polarized tunnel ferromagnetic junctions. Experimental data are consistent with a progressive enhancement of the magnetic activity with the increase of the barrier thickness, as neatly captured by the simplest theoretical approach including a nonuniform exchange field. For very long junctions, unconventional magnetic activity of the barrier points to the presence of spin-triplet correlations
Electrodynamics of Josephson junctions containing strong ferromagnets
Triplet supercurrents in multilayer ferromagnetic Josephson junctions with misaligned magnetization survive longer barrier thicknesses when compared with singlet supercurrents. The distinctive feature of triplet supercurrents is the scaling of the characteristic voltage of the junction with increasing ferromagnetic barrier thickness - an algebraic decay in contrast to an exponential decay for singlet supercurrents. Although the static properties of these junctions have been extensively studied, the dynamic characteristics remain largely unexplored. Here we report a comprehensive electrodynamic characterization of multilayer ferromagnetic Josephson junctions composed of Co and Ho. By measuring the temperature-dependent current-voltage characteristics and the switching current distributions down to 0.3 K, we show that phase dynamics of junctions with triplet supercurrents exhibits long (in terms of proximity) junction behavior and moderately damped dynamics with renormalized capacitance and resistance. This unconventional behavior possibly provides a different way to dynamically detect triplets. Our results show that new theoretical models are required to fully understand the phase dynamics of triplet Josephson junctions for applications in superconducting spintronics
- âŠ