Dynamics of combined electron beam and laser dispersion of polymers in vacuum

The mechanisms of the impact of the laser assisting effect on the dispersion kinetics and on the structure of the deposited layers in electron beam dispersion of a polymer target were analyzed. The proposed model and analytical expressions adequately describe the kinetic dependence of the polymer materials dispersion rate in a vacuum on the intensity of laser processing of their dispersion zone

Adaptive observers for nonlinearly parameterized systems subjected to parametric constraints

We consider the problem of adaptive observer design in the settings when the system is allowed to be nonlinear in the parameters, and furthermore they are to satisfy additional feasibility constraints. A solution to the problem is proposed that is based on the idea of universal observers and non-uniform small-gain theorem. The procedure is illustrated with an example.Comment: 19th IFAC World Congress on Automatic Control, 10869-10874, South Africa, Cape Town, 24th-29th August, 201

Enhancing superconductivity: Magnetic impurities and their quenching by magnetic fields

Magnetic fields and magnetic impurities are each known to suppress superconductivity. However, as the field quenches (i.e. polarizes) the impurities, rich consequences, including field-enhanced superconductivity, can emerge when both effects are present. For the case of superconducting wires and thin films, this field-spin interplay is investigated via the Eilenberger-Usadel scheme. Non-monotonic dependence of the critical current on the field (and therefore field-enhanced superconductivity) is found to be possible, even in parameter regimes in which the critical temperature decreases monotonically with increasing field. The present work complements that of Kharitonov and Feigel'man, which predicts non-monotonic behavior of the critical temperature.Comment: 8 pages, 2 figures, EPL forma

Superconductor Insulator Transition in Long MoGe Nanowires

Properties of one-dimensional superconducting wires depend on physical processes with different characteristic lengths. To identify the process dominant in the critical regime we have studied trans- port properties of very narrow (9-20 nm) MoGe wires fabricated by advanced electron-beam lithography in wide range of lengths, 1-25 microns. We observed that the wires undergo a superconductor -insulator transition that is controlled by cross sectional area of a wire and possibly also by the thickness-to-width ratio. Mean-field critical temperature decreases exponentially with the inverse of the wire cross section. We observed that qualitatively similar superconductor{insulator transition can be induced by external magnetic field. Some of our long superconducting MoGe nanowires can be identified as localized superconductors, namely in these wires one-electron localization length is much shorter than the length of a wire

Determination of the Superconductor-Insulator Phase Diagram for One-Dimensional Wires

We establish the superconductor-insulator phase diagram for quasi-one dimensional wires by measuring a large set of MoGe nanowires. This diagram is consistent with the Chakravarty-Schmid-Bulgadaev phase boundary, namely with the critical resistance being equal to R_Q = h/4e^2. We find that transport properties of insulating nanowires exhibit a weak Coulomb blockade behavior.Comment: 5 pages, 4 figure

Magnetic field enhancement of superconductivity in ultra-narrow wires

We study the effect of an applied magnetic field on sub-10nm wide MoGe and Nb superconducting wires. We find that magnetic fields can enhance the critical supercurrent at low temperatures, and does so more strongly for narrower wires. We conjecture that magnetic moments are present, but their pair-breaking effect, active at lower magnetic fields, is suppressed by higher fields. The corresponding microscopic theory, which we have developed, quantitatively explains all experimental observations, and suggests that magnetic moments have formed on the wire surfaces.Comment: 4 pages, 3 figures, 1 tabl

Influence of high magnetic fields on superconducting transition of one-dimensional Nb and MoGe nanowires

The effects of strong magnetic field on superconducting Nb and MoGe nanowires with diameter $\sim10$ nm have been studied. We have found that the Langer-Ambegaokar-McCumber-Halperin (LAMH) theory of thermally activated phase slips is applicable in a wide range of magnetic fields and describes well the temperature dependence of the wire resistance, over eleven orders of magnitude. The field dependence of the critical temperature, $T_{c}$, extracted from the LAMH fits is in good quantitative agreement with the theory of pair-breaking perturbations that takes into account both spin and orbital contributions. The extracted spin-orbit scattering time agrees with an estimate $\tau_{so}\simeq \tau(\hbar c/ Ze^{2})^{4}$, where $\tau$ is the elastic scattering time and $Z$ is the atomic number.Comment: accepted for publication in Physical Review Letter