Effect of ferromagnetic film thickness on magnetoresistance of thin-film superconductor-ferromagnet hybrids

We study the influence of the thickness Df of the plain ferromagnetic (F) film on the electrical resistance of the flux-coupled hybrids, consisting of superconducting (S) Al film and multilayer [Co/Pt] F film with out-of-plain magnetization. The behavior of such hybrids at high and low temperatures is found to be different: the nucleation of superconductivity at high temperatures is governed mainly by the typical lateral dimensions of the magnetic domains, while low temperature properties are determined by topology of the magnetic template. We show that an increase in the Df value leads to a broadening of the field- and temperature intervals where non-monotonous dependence of the superconducting critical temperature Tc on the applied magnetic field H is observed (for demagnetized F films). Further increase in the Df value results in a global suppression of superconductivity. Thus, we determined an optimal thickness, when the non-monotonous dependence Tc(H) can be observed in rather broad T and H range, what can be interesting for further studies of the localized superconductivity in planar Al-based S/F hybrids and for development of the devices which can exploit the localized superconductivity.Comment: 10 pages, 9 figure

Sonoluminescence and collapse dynamics of multielectron bubbles in helium

Multielectron bubbles (MEBs) differ from gas-filled bubbles in that it is the Coulomb repulsion of a nanometer thin layer of electrons that forces the bubble open rather than the pressure of an enclosed gas. We analyze the implosion of MEBs subjected to a pressure step, and find that despite the difference in the underlying processes the collapse dynamics is similar to that of gas-filled bubbles. When the MEB collapses, the electrons inside it undergo strong accelerations, leading to the emission of radiation. This type of sonoluminescence does not involve heating and ionisation of any gas inside the bubble. We investigate the conditions necessary to obtain sonoluminescence from multielectron bubbles and calculate the power spectrum of the emitted radiation.Comment: 6 figure

Electric field induced strong localization of electrons on solid hydrogen surface: possible applications to quantum computing

Two-dimensional electron system on the liquid helium surface is one of the leading candidates for constructing large analog quantum computers (P.M. Platzman and M.I. Dykman, Science 284, 1967 (1999)). Similar electron systems on the surfaces of solid hydrogen or solid neon may have some important advantages with respect to electrons on liquid helium in quantum computing applications, such as larger state separation $\Delta E$, absence of propagating capillary waves (or ripplons), smaller vapor pressure, etc. As a result, it may operate at higher temperatures. Surface roughness is the main hurdle to overcome in building a realistic quantum computer using these states. Electric field induced strong localization of surface electrons is shown to be a convenient tool to characterize surface roughness.Comment: 4 pages, 3 figure

The effect of the probe magnetic moment orientation of magnetic resonance force microscope on the spectra of spin wave resonances

This work was supported by the Russian Science Foundation (project 16-12-10254)

Charged-Surface Instability Development in Liquid Helium; Exact Solutions

The nonlinear dynamics of charged-surface instability development was investigated for liquid helium far above the critical point. It is found that, if the surface charge completely screens the field above the surface, the equations of three-dimensional (3D) potential motion of a fluid are reduced to the well-known equations describing the 3D Laplacian growth process. The integrability of these equations in 2D geometry allows the analytic description of the free-surface evolution up to the formation of cuspidal singularities at the surface.Comment: latex, 5 pages, no figure

Equilibrium properties of the mixed state in superconducting niobium in a transverse magnetic field: Experiment and theoretical model

Equilibrium magnetic properties of the mixed state in type-II superconductors were measured with high purity bulk and film niobium samples in parallel and perpendicular magnetic fields using dc magnetometry and scanning Hall-probe microscopy. Equilibrium magnetization data for the perpendicular geometry were obtained for the first time. It was found that none of the existing theories is consistent with these new data. To address this problem, a theoretical model is developed and experimentally validated. The new model describes the mixed state in an averaged limit, i.e. %without detailing the samples' magnetic structure and therefore ignoring interactions between vortices. It is quantitatively consistent with the data obtained in a perpendicular field and provides new insights on properties of vortices. % and the entire mixed state. At low values of the Ginzburg-Landau parameter, the model converts to that of Peierls and London for the intermediate state in type-I superconductors. It is shown that description of the vortex matter in superconductors in terms of a 2D gas is more appropriate than the frequently used crystal- and glass-like scenarios.Comment: 8 pages, 9 figure

INTERNATIONAL MARKET EXPANSION

In article various theoretical aspects of an exit of the companies on the foreign markets are considered. Influence of globalization on productivity of the companies is considered, ways and factors of a choice of strategy of an exit to the world market are analysed. The behavioural and cultural aspects influencing strategy of an exit to the world market are analysed. The analysis of strategy of the companies which have entered the foreign markets, is carried out taking into account the previous researches in this area.The following conclusions became result of research: 1) globalization positively influences the companies as the market increases, however the small companies and the companies in emerging markets lose in competitive fight; 2) the companies with considerable experience are inclined to choose strategy of opening of own enterprise while the organizations without similar experience prefer export or joint venture in the host country territory; 3) the strategy choice with a bigger involvement of resources is directly proportional to knowledge of culture of the country to which there is a company. At entry into the market with other culture smooth adaptation is necessary for successful realization of strategy. At last, people are inclined to make behavioural mistakes, and knowledge of them and continuous control will help to achieve successful results; 4) for an exit and successful work in the foreign markets of the company important not only to possess competences, but also to be able to protect them and to keep in time; 5) on the market with high political and investment risks, and also adverse economic conditions of the company are inclined to choose strategy with the minimum investment of money (franchizes, licensing)

Amplification of Fluctuations in Unstable Systems with Disorder

We study the early-stage kinetics of thermodynamically unstable systems with quenched disorder. We show analytically that the growth of initial fluctuations is amplified by the presence of disorder. This is confirmed by numerical simulations of morphological phase separation (MPS) in thin liquid films and spinodal decomposition (SD) in binary mixtures. We also discuss the experimental implications of our results.Comment: 15 pages, 4 figure

Microwave saturation of the Rydberg states of electrons on helium

We present measurements of the resonant microwave excitation of the Rydberg energy levels of surface state electrons on superfluid helium. The temperature dependent linewidth agrees well with theoretical predictions and is very small below 300 mK. Absorption saturation and power broadening were observed as the fraction of electrons in the first excited state was increased to 0.49, close to the thermal excitation limit of 0.5. The Rabi frequency was determined as a function of microwave power. The high values of the ratio of the Rabi frequency to linewidth confirm this system as an excellent candidate for creating qubits.Comment: 4 pages, 4 figure

Eye Hydrodynamics after Combined Treatment of Primary Open-Angle Glaucoma and Complicated Cataract

Aim: To study hydrodynamics of the eye after combined treatment – a combination of laser activation of trabecula and cataract phacoemulsification – in a comparative aspect.Material and methods. The study included 65 patients (65 eyes) with initial and advanced stages (I–II stages) of primary open-angle glaucoma (POAG) and complicated cataract. Among the patients there were 38 women (58.5 %) and 27 men (41.5 %), the average age was 68.8 ± 8.2 years. The follow-up period is 12 months after the treatment. The patients were divided into two groups: the main one – 33 patients (33 eyes) who underwent combined treatment – YAG-laser activation of trabecula (YAG-LAT) and phacoemulsification of cataract with intraocular lens (IOL) implantation, the control group – 32 patients (32 eyes) who underwent only phacoemulsification.Initially, the average intraocular pressure (IOP) (P0) in the main and control groups was 20.72 ± 3.39 mm Hg and 21.02 ± 3.55 mm Hg respectively. The average number of antihypertensive drugs used in the study group was 1.53 ± 0.64, in the control group – 1.34 ± 0.55.Results. There were no intraand postoperative complications. By the end of the follow-up period, a significant decrease in the average IOP level compared to its preoperative value by 29.2 % was determined in the main group, and 9.8 % in the control. The average number of antihypertensive drugs used in the study group decreased from 1.53 ± 0.64 to 0.67 ± 0.59 (p < 0.05), in the control group of patients, on the contrary, the average number of antihypertensive agents increased from 1.34 ± 0.55 to 1.91 ± 0.70 (p < 0.05).Conclusion. In the long-term postoperative period after combined treatment (YAG-LAT + phaco), IOP normalization was achieved in 96.9 % of cases, as well as a significant increase in visual acuity of patients. The developed method of treatment is safe, has a minimal risk of complications and can be used for the treatment of patients with initial stages of POAG in combination with complicated cataracts with increased IOP level, inefficiency of antihypertensive therapy