1,494 research outputs found
Fabrication of high quality ferromagnetic Josephson junctions
We present ferromagnetic Nb/Al2O3/Ni60Cu40/Nb Josephson junctions (SIFS) with
an ultrathin Al2O3 tunnel barrier. The junction fabrication was optimized
regarding junction insulation and homogeneity of current transport. Using
ion-beam-etching and anodic oxidation we defined and insulated the junction
mesas. The additional 2 nm thin Cu layer below the ferromagnetic NiCu (SINFS)
lowered interface roughness and ensured very homogeneous current transport. A
high yield of junctional devices with jc spreads less than 2% was obtained.Comment: 5 pages, 6 figures; VORTEX IV conference contribution; Submitted to
Physica
Strong enhancement of direct magnetoelectric effect in strained ferroelectric-ferromagnetic thin-film heterostructures
The direct magnetoelectric (ME) effect resulting from the polarization
changes induced in a ferroelectric film by the application of a magnetic field
to a ferromagnetic substrate is described using the nonlinear thermodynamic
theory. It is shown that the ME response strongly depends on the initial strain
state of the film. The ME polarization coefficient of the heterostructures
involving Terfenol-D substrates and compressively strained lead zirconate
titanate (PZT) films, which stabilize in the out-of-plane polarization state,
is found to be comparable to that of bulk PZT/Terfenol-D laminate composites.
At the same time, the ME voltage coefficient reaches a giant value of 50 V/(cm
Oe), which greatly exceeds the maximum observed static ME coefficients of bulk
composites. This remarkable feature is explained by a favorable combination of
considerable strain sensitivity of polarization and a low electric permittivity
in compressively strained PZT films. The theory also predicts a further
dramatic increase of ME coefficients at the strain-induced transitions between
different ferroelectric phases.Comment: 7 pages, 3 figure
GC-MS-based 13C metabolic flux analysis resolves the parallel and cyclic glucose metabolism of Pseudomonas putida KT2440 and Pseudomonas aeruginosa PAO1
The genus Pseudomonas comprises approximately 200 species with numerous isolates that are common inhabitants of soil, water, and vegetation and has been of particular interest for more than one hundred years. Here, we present a novel approach for accurate, precise and convenient 13C metabolic flux analysis of these and other microbes possessing periplasmic glucose oxidation and a cyclic hexose metabolism, which forms the recently discovered EDEMP cycle. This complex cyclic architecture cannot be resolved by common metabolic flux workflows, which rely on GC-MS-based labelling analysis of proteinogenic amino acids. Computational analyses revealed that this limitation can be overcome by three parallel labelling experiments on specific tracers, i.e., [1-13C], [6-13C] and 50% [13C6] glucose, with additional consideration of labelling information from glucose and glucosamine. Glucose and glucosamine display building blocks from cellular glycogen, peptidoglycan and lipopolysaccharides, reflect the pools of glucose6-phosphate and fructose6-phosphate in the heart of the EDEMP cycle and as we show, can be precisely assessed in biomass hydrolysates by GC-MS. The developed setup created 534 mass isotopomers and enabled high-resolution flux analysis of the cell factory Pseudomonas putida KT2440 and the human pathogen P. aeruginosa PAO1. The latter strain oxidized approximately 90% of its glucose into gluconate via the periplasmic route, whereas only a small fraction of substrate was phosphorylated and consumed via the cytoplasmic route. The oxidative pentose phosphate pathway was completely inactive, indicating the essentiality of the Entner-Doudoroff pathway and recycling of triose units into anabolic precursors. In addition to pseudomonads, many microbes operate a cyclic hexose metabolism, which becomes more accessible to flux analysis with this approach. In this regard, the presented approach displays a valuable extension of the available set of flux methods for these types of bacteria
Observation of Josephson coupling through an interlayer of antiferromagnetically ordered chromium
The supercurrent transport in metallic Josephson tunnel junctions with an
additional interlayer made up by chromium, being an itinerant antiferromagnet,
was studied. Uniform Josephson coupling was observed as a function of the
magnetic field. The supercurrent shows a weak dependence on the interlayer
thickness for thin chromium layers and decays exponentially for thicker films.
The diffusion constant and the coherence length in the antiferromagnet were
estimated. The antiferromagnetic state of the barrier was indirectly verified
using reference samples. Our results are compared to macroscopic and
microscopic models.Comment: Phys. Rev. B (2009), in prin
Memory cell based on a Josephson junction
The Josephson junction has a doubly degenerate ground state with
the Josephson phases . We demonstrate the use of such a
Josephson junction as a memory cell (classical bit), where writing is done by
applying a magnetic field and reading by applying a bias current. In the
"store" state, the junction does not require any bias or magnetic field, but
just needs to stay cooled for permanent storage of the logical bit.
Straightforward integration with Rapid Single Flux Quantum logic is possible.Comment: to be published in AP
Spontaneous chirality via long-range electrostatic forces
We consider a model for periodic patterns of charges constrained over a
cylindrical surface. In particular we focus on patterns of chiral helices,
achiral rings or vertical lamellae, with the constraint of global
electroneutrality. We study the dependence of the patterns' size and pitch
angle on the radius of the cylinder and salt concentration. We obtain a phase
diagram by using numerical and analytic techniques. For pure Coulomb
interactions, we find a ring phase for small radii and a chiral helical phase
for large radii. At a critical salt concentration, the characteristic domain
size diverges, resulting in macroscopic phase segregation of the components and
restoring chiral symmetry. We discuss possible consequences and generalizations
of our model.Comment: Revtex, 4 pages, 4 figure
Low-T_c Josephson junctions with tailored barrier
Nb/Al_2O_3/Ni_{0.6}Cu_{0.4}/Nb based
superconductor-insulator-ferromagnet-superconductor (SIFS) Josephson tunnel
junctions with a thickness step in the metallic ferromagnetic
\Ni_{0.6}\Cu_{0.4} interlayer were fabricated. The step was defined by optical
lithography and controlled etching. The step height is on the scale of a few
angstroms. Experimentally determined junction parameters by current-voltage
characteristics and Fraunhofer pattern indicate an uniform F-layer thickness
and the same interface transparencies for etched and non-etched F-layers. This
technique could be used to tailor low-T_c Josephson junctions having controlled
critical current densities at defined parts of the junction area, as needed for
tunable resonators, magnetic-field driven electronics or phase modulated
devices.Comment: 6 pages, 6 figures, small changes, to be published by JA
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