Josephson current in superconductor-ferromagnet structures with a nonhomogeneous magnetization

We calculate the dc Josephson current $I_J$ for two types of superconductor-ferromagnet (S/F) Josephson junctions. The junction of the first type is a S/F/S junction. On the basis of the Eilenberger equation, the Josephson current is calculated for an arbitrary impurity concentration. If $h\tau\ll1$ the expression for the Josephson critical current $I_c$ is reduced to that which can be obtained from the Usadel equation ($h$ is the exchange energy, $\tau$ is the momentum relaxation time). In the opposite limit $h\tau\gg1$ the superconducting condensate oscillates with period $$ and penetrates into the F region over distances of the order of the mean free path $l$. For this kind of junctions we also calculate $I_J$ in the case when the F layer presents a nonhomogeneous (spiral) magnetic structure with the period $2\pi /Q$. It is shown that for not too low temperatures, the $\pi$-state which occurs in the case of a homogeneous magnetization (Q=0) may disappear even at small values of $Q$. In this nonhomogeneous case, the superconducting condensate has a nonzero triplet component and can penetrate into the F layer over a long distance of the order of $\xi_{T}=$. The junction of the second type consists of two S/F bilayers separated by a thin insulating film. It is shown that the critical Josephson current $I_{c}$ depends on the relative orientation of the effective exchange field $h$ of the bilayers. In the case of an antiparallel orientation, $I_{c}$ increases with increasing $h$. We establish also that in the F film deposited on a superconductor, the Meissner current created by the internal magnetic field may be both diamagnetic or paramagnetic.Comment: 13 pages, 11 figures. To be published in Phys. Rev.

Особенности рекреационного потенциала лесных биогеоценозов Клинско-Дмитровской гряды

The article is devoted to recreational opportunities of forest ecosystems of Clinsko-Dmytrovskaja Grjada. Recreational potential in connection of forest types was given as result of male study. As a result of studies is assessed the recreational potential in relation to forest types. The impact of various forms of rechation on the state of the main elements of the forest has been given. The description of flora and fauna have been given.Статья посвящена выявлению рекреационных возможностей лесных биогеоценозов Клинско-Дмитровской гряды. В результате проведенных исследований была дана оценка рекреационного потенциала в связи с типами леса. Выявлено воздействие различных форм рекреации на состояние основных элементов леса. Приведено описание флоры и фауны объекта исследования

Giant thermoemf in multiterminal superconductor/normal metal mesoscopic structures

We considered a mesoscopic superconductor/normal metal (S/N) structure in which the N reservoirs are maintained at different temperatures. It is shown that in the absence of current between the N reservoirs a voltage difference $V_{T}$ arises between the superconducting and normal conductors. The voltage $V_{T}$ oscillates with increasing phase difference $\phi$ between the superconductors, and its magnitude does not depend on the small parameter $(T/\epsilon_{F}).$Comment: Resubmited, some changes to Text and Figure

Nonequilibrium Josephson effect in short-arm diffusive SNS interferometers

We study non-equilibrium Josephson effect and phase-dependent conductance in three-terminal diffusive interferometers with short arms. We consider strong proximity effect and investigate an interplay of dissipative and Josephson currents co-existing within the same proximity region. In junctions with transparent interfaces, the suppression of the Josephson current appears at rather large voltage, $eV\sim \Delta$, and the current vanishes at $eV\geq\Delta$. Josephson current inversion becomes possible in junctions with resistive interfaces, where the inversion occurs within a finite interval of the applied voltage. Due to the presence of considerably large and phase-dependent injection current, the critical current measured in a current biased junction does not coincide with the maximum Josephson current, and remains finite when the true Josephson current is suppressed. The voltage dependence of the conductance shows two pronounced peaks, at the bulk gap energy, and at the proximity gap energy; the phase oscillation of the conductance exhibits qualitatively different form at small voltage $eV<\Delta$, and at large voltage $eV>\Delta$.Comment: 11 pages, 9 figures, revised version, to be published in Phys. Rev.

Local density of states in superconductor-strong ferromagnet structures

We study the dependence of the local density of states (LDOS) on coordinates for a superconductor-ferromagnet (S/F) bilayer and a S/F/S structure assuming that the exchange energy h in the ferromagnet is sufficiently large: $>>1,$ where $\tau$ is the elastic relaxation time. This limit cannot be described by the Usadel equation and we solve the more general Eilenberger equation. We demonstrate that, in the main approximation in the parameter $(h\tau)^{-1}$, the proximity effect does not lead to a modification of the LDOS in the S/F system and a non-trivial dependence on coordinates shows up in next orders in $(h\tau) ^{-1}.$ In the S/F/S sandwich the correction to the LDOS is nonzero in the main approximation and depends on the phase difference between the superconductors. We also calculate the superconducting critical temperature $T_{c}$ for the bilayered system and show that it does not depend on the exchange energy of the ferromagnet in the limit of large h and a thick F layer.Comment: 9 pages, 5 figure

Synthesis of Mn2+-doped CdS nanoparticles covered with different adsorptive layers and their application as biosensors

Colloidal CdS:Mn nanoparticles were synthesized in water solutions of the polymer polyvinyl-pyrrolidone (PVP), the surfactant cetyl-trimethyl-ammonium bromide (CTAB) and the mixture of PVP and CTAB. The sizes of nanoparticles were determined by electron microscopy and optical absorption methods. The growth media influence on photoluminescence of nanoparticles has been studied. It has been shown that the chemical composition and structure of the adsorptive layer on the surface of nanoparticles can be used as a technological tool to control their light emission. The possibility to use CdS:Mn NPs grown in PVP as light-emitting labels in biological media has been demonstrated

Coherent Charge Transport in Metallic Proximity Structures

We develop a detailed microscopic analysis of electron transport in normal diffusive conductors in the presence of proximity induced superconducting correlation. We calculated the linear conductance of the system, the profile of the electric field and the densities of states. In the case of transparent metallic boundaries the temperature dependent conductance has a non-monotoneous ``reentrant'' structure. We argue that this behavior is due to nonequilibrium effects occuring in the normal metal in the presence of both superconducting correlations and the electric field there. Low transparent tunnel barriers suppress the nonequilibrium effects and destroy the reentrant behavior of the conductance. If the wire contains a loop, the conductance shows Aharonov-Bohm oscillations with the period $\Phi_0=h/2e$ as a function of the magnetic flux $\Phi$ inside the loop. The amplitude of these oscillations also demonstrates the reentrant behavior vanishing at $T=0$ and decaying as $1/T$ at relatively large temperatures. The latter behavior is due to low energy correlated electrons which penetrate deep into the normal metal and ``feel'' the effect of the magnetic flux $\Phi$. We point out that the density of states and thus the ``strengh'' of the proximity effect can be tuned by the value of the flux inside the loop. Our results are fully consistent with recent experimental findings.Comment: 16 pages RevTeX, 23 Postscript figures, submitted to Phys. Rev.