4,789 research outputs found
Tunable pinning in superconducting films with magnetic micro-loops
We study the flux pinning properties of superconductor/magnetic micro-rings
lattice hybrid structures. The used open triangular micromagnets represent an
eight-fold degree of freedom system, with six polarized and two flux-closure
possible states. By conveniently choosing the magnetic state of the underlying
rings it is possible to induce different pinning potentials. We show that the
magnetic vortex state with minimum stray field produces a weaker pinning in
comparison with the polarized states
A multicarrier amplifier design linearized trough second harmonics and second-order IM feedback
A novel linearisation technique for reduction in the
first and second kind of the third-order intermodulation
products was applied in this paper. The second harmonics and
second-order intermodulation products are led from the output to the input of a power amplifier through a feedback loop. The power amplifier including the feedback loop components (bandpass filter, phase shifter and attenuator) was designed as a hybrid microwave integrated circuit by using program ADS. The phase and amplitude of the loop signals are the adjustable parameters. Therefore, a voltage that controls a phase shift of the phase shifter and a control current of a PIN diode in the attenuator circuit were optimised to obtain a reduction in the third-order intermodulation distortion. For three fundamental signals at the power amplifier input, the lowest improvement of 13 dB for the first and 18 dB for the second kind of the third order intermodulation product levels was achieved
Topological quantization of energy transport in micro- and nano-mechanical lattices
Topological effects typically discussed in the context of quantum physics are
emerging as one of the central paradigms of physics. Here, we demonstrate the
role of topology in energy transport through dimerized micro- and
nano-mechanical lattices in the classical regime, i.e., essentially "masses and
springs". We show that the thermal conductance factorizes into topological and
non-topological components. The former takes on three discrete values and
arises due to the appearance of edge modes that prevent good contact between
the heat reservoirs and the bulk, giving a length-independent reduction of the
conductance. In essence, energy input at the boundary mostly stays there, an
effect robust against disorder and nonlinearity. These results bridge two
seemingly disconnected disciplines of physics, namely topology and thermal
transport, and suggest ways to engineer thermal contacts, opening a direction
to explore the ramifications of topological properties on nanoscale technology.Comment: 6 pages, 3 figures; Supplemental information included as an ancillary
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Silicon Waveguides and Ring Resonators at 5.5 {\mu}m
We demonstrate low loss ridge waveguides and the first ring resonators for
the mid-infrared, for wavelengths ranging from 5.4 to 5.6 {\mu}m. Structures
were fabricated using electron-beam lithography on the silicon-on-sapphire
material system. Waveguide losses of 4.0 +/- 0.7 dB/cm are achieved, as well as
Q-values of 3.0 k.Comment: 4 pages, 4 figures, includes supplemental material
Magnetic dipole induced guided vortex motion
We present evidence of magnetically controlled guided vortex motion in a
hybrid superconductor/ferromagnet nanosystem consisting of an Al film on top of
a square array of permalloy square rings. When the rings are magnetized with an
in-plane external field H, an array of point-like dipoles with moments
antiparallel to H, is formed. The resulting magnetic template generates a
strongly anisotropic pinning potential landscape for vortices in the
superconducting layer. Transport measurements show that this anisotropy is able
to confine the flux motion along the high symmetry axes of the square lattice
of dipoles. This guided vortex motion can be either re-routed by 90 degrees by
simply changing the dipole orientation or even strongly suppressed by inducing
a flux-closure magnetic state with very low stray fields in the rings.Comment: 5 pages, 3 figure
Linearization of multichannel amplifiers with the injection of second harmonics into the amplifier and predistortion circuit
A linearization technique that uses the injection of the fundamental signal second harmonics together with the fundamental signals at the amplifier input has been extended in this paper by introducing the injection the second harmonics into nonlinear microwave amplifier and so-called predistortion circuit. Predistortion circuit produces the third-order intermodulation signals that are injected at the amplifier input together with the second harmonics making the linearization procedure more independent on the phase variation of the second harmonics. In addition, a considerably better improvement is attained for the power of fundamental signals close to 1-dB compression point by applying the linearization technique proposed in this paper in comparison to the linearization with the injection of the second harmonics merely in the nonlinear amplifier
Self organized mode locking effect in superconductor / ferromagnet hybrids
The vortex dynamics in a low temperature superconductor deposited on top of a
rectangular array of micrometer size permalloy triangles is investigated
experimentally. The rectangular unit cell is such that neighboring triangles
physically touch each other along one direction. This design stabilizes
remanent states which differ from the magnetic vortex state typical of
individual non-interacting triangles. Magnetic Force Microscopy images have
revealed that the magnetic landscape of the template can be switched to an
ordered configuration after magnetizing the sample with an in-plane field. The
ordered phase exhibits a broad flux flow regime with relatively low critical
current and a highly anisotropic response. This behavior is caused by the
spontaneous formation of two separated rows of vortices and antivortices along
each line of connected triangles. The existence of a clear flux flow regime
even for zero external field supports this interpretation. The density of
induced vortex-antivortex pairs is directly obtained using a high frequency
measurement technique which allows us to resolve the discrete motion of
vortices. Strikingly, the presence of vortex-antivortex rows gives rise to a
self organized synchronized motion of vortices which manifests itself as field
independent Shapiro steps in the current-voltage characteristics.Comment: 9 pages, 11 figure
Domain wall displacement in Py square ring for single nanometric magnetic bead detection
A new approach based on the domain wall displacement in confined
ferromagnetic nanostructures for attracting and sensing a single nanometric
magnetic particles is presented. We modeled and experimentally demonstrated the
viability of the approach using an anisotropic magnetoresistance device made by
a micron-size square ring of Permalloy designed for application in magnetic
storage. This detection concept can be suitable to biomolecular recognition,
and in particular to single molecule detection.Comment: 8pages, 3figure
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