Перегляд за Автор "Shklovskij, V.A."

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Current-controlled filter on superconducting films with a tilted washboard pinning potential
(Elsevier, 2012) Dobrovolskiy, O.V.; Shklovskij, V.A.; Huth, M.
The influence of an ac current of arbitrary amplitude and frequency on the mixed-state dc-voltage-ac-drive tiltingratchet response of a superconducting film with uniaxial cosine pinning potential at finite temperature is theoretically investigated. The results are obtained in the single-vortex approximation, within the frame of an exact solution of the Langevin equation for non-interacting vortices. Both experimentally achievable, the dc ratchet response and absorbed ac power are predicted to demonstrate a pronounced filter-like behavior at microwave frequencies. Based on our findings, we propose a cut-off filter and discuss its operating curves as functions of the driving parameters, i.e, ac amplitude, frequency, and dc bias. The predicted results can be examined, e.g, on superconducting films with a washboard pinning potential landscape.
Material composition – Pinning strength correlation in Nb thin films with focused ion beam-milled washboard nanostructures
(Physica C, 2013-03-29) Dobrovolskiy, O.V.; Begun, Evgenia; Huth, M.; Shklovskij, V.A.
An analysis of the interrelated changes in the material composition and the pinning strength in nanostructured Nb (110) thin films is presented. The nanopatterns were prepared by focused ion beam milling of an array of uniaxial grooves. They induce a washboard-like pinning potential landscape for vortices in the mixed state. By applying different magnetic fields, the most likely pinning sites along which the flux lines move through the samples have been selected. By this, either the background isotropic pinning of the pristine film or the enhanced isotropic pinning originating from the nanoprocessing has been probed. The enhanced pinning strength in the processed films has been found to correlate with the content of Ga implanted into the films during the nanopatterning.
Microwave Absorption by Vortices in Superconductors with a Washboard Pinning Potential
(Intech, 2012) Shklovskij, V.A.; Dobrovolskiy, O.V.
let us compare the results presented in the chapter with the analogous but more general results obtained by the authors [25] on the basis of a stochastic model for arbitrary temperature T and densities j0 and j1. In that work, the Langevin equation (1), supplemented with a thermofluctuation term, has been exactly solved for γ = 1 interms ofamatrix continued fraction [52] and, depending on the WPP’s tilt caused by the dc current, two substantially differentmodes in the vortexmotion have been predicted. Inmore detail, at low temperatures and relatively high frequencies in a nontilted pinning potential each pinned vortex is confined to its pinning potential well during the ac period. In the case of superimposed strong ac and dc driving currents a running state of the vortex may appear when it can visit several (or many) potential wells during the ac period. As a result, two branches of new findings have been elucidated [25, 27]. First, the influence of an ac current on the usual E0(j0) and ratchet E0(j1) CVCs has been analyzed. Second, the influence of a dc current on the ac nonlinear impedance response and nonlinear power absorption has been investigated. In particular, the appearance of Shapiro-like steps in the usual CVC and the appearance of phase-locking regions in the ratchet CVC has been predicted. At the same time, it has been shown that an anomalous power absorption in the ac response is expected at close-to critical currents j0 jc and relatively low frequencies ω ωp. Figure 8 shows the main predictions of these works. Namely, predicted are (i) an enhanced power absorption at low frequencies, (ii) a temperature- and current-dependent minimum at intermediate frequencies. (iii) At substantially low temperatures, the absorption can acquire negative values which physically corresponds to the generation by vortices. However, a more general and formally precise solution of the problem in terms of a matrix-continued fraction does not allow the main physical results of the problemto be investigated in the formof explicit analytical functions of the main physical quantities (j0, j1, ω, α, T, , and γ) which, we believe, has helped us greatly to elucidate the physics in the problem under consideration.
Noise-Assisted Microwave Up-conversion by Vortices in Thin-Film Superconductors with a dc-Biased Washboard Pinning Potential
(Springer Science+Business Media New York 2012, 2012-12-20) Shklovskij, V.A.; Dobrovolskiy, O.V.; Huth, M.
So far the main theoretical basis for understanding and optimization of the microwave properties of vortices in type II superconductors has been relying upon the Coffey–Clem (CC) approach for the linear impedance at nonzero temperature. However, the CC model does not account for the non-linear response and the possibility to control it by changing the value of the dc transport current in a superconducting sample. For this reason, we have exactly solved the Langevin equation for the two-dimensional nonlinear vortex dynamics in a dc bias-tilted cosine pinning potential in the presence of an ac current of arbitrary amplitude and frequency ω and have, thereby, substantially generalized the CC results. In this work we analyze the behavior of the non-linear response on kω-frequency in a wide range of dc and ac current densities, ω, and temperature. The kω- response is found to depend strongly on all these parameters, as exemplified for the third-harmonic (k = 3) transformation coefficient Z3. The parametric window for the most enhanced up-conversion is presented. The predicted effects can be experimentally verified in thin-film superconductors with some pinning potential of the washboard type.