Microscopic nonequilibrium theory of double-barrier Josephson junctions

We study nonequilibrium charge transport in a double-barrier Josephson junction, including nonstationary phenomena, using the time-dependent quasiclassical Keldysh Green's function formalism. We supplement the kinetic equations by appropriate time-dependent boundary conditions and solve the time-dependent problem in a number of regimes. From the solutions, current-voltage characteristics are derived. It is understood why the quasiparticle current can show excess current as well as deficit current and how the subgap conductance behaves as function of junction parameters. A time-dependent nonequilibrium contribution to the distribution function is found to cause a non-zero averaged supercurrent even in the presence of an applied voltage. Energy relaxation due to inelastic scattering in the interlayer has a prominent role in determining the transport properties of double-barrier junctions. Actual inelastic scattering parameters are derived from experiments. It is shown as an application of the microscopic model, how the nature of the intrinsic shunt in double-barrier junctions can be explained in terms of energy relaxation and the opening of Andreev channels.Comment: Accepted for Phys. Rev.

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.

Hydrodynamic fluctuations of a liquid with anisotropic molecules

A general theory of hydrodynamic fluctuations of a liquid with anisotropic molecules, in the presence of steady simple shear, has been proposed.Comment: 19 pages, to be published in Physica A, Sept. 200

Impurity band in clean superconducting weak links

Weak impurity scattering produces a narrow band with a finite density of states near the phase difference $\phi =\pi$ in the mid-gap energy spectrum of a macroscopic superconducting weak link. The equivalent distribution of transmission coefficients of various cunducting quantum channels is found.Comment: 4 pages, 4 figures, changed conten

Effect of point-contact transparency on coherent mixing of Josephson and transport supercurrents

The influence of electron reflection on dc Josephson effect in a ballistic point contact with transport current in the banks is considered theoretically. The effect of finite transparency on the vortex-like currents near the contact and at the phase difference $\phi =\pi ,$ which has been predicted recently \cite{KOSh}, is investigated. We show that at low temperatures even a small reflection on the contact destroys the mentioned vortex-like current states, which can be restored by increasing of the temperature.Comment: 6 pages, 8 Figures, Latex Fil

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

Вплив жорсткого ультрафіолету на структуру та оптичні властивості шарів CdS та CdTe

The influence of hard ultraviolet radiation on the crystalline structure, surface morphology and optical characteristics of CdS and CdTe semiconductor layers obtained by direct current magnetron sputtering are investigated. It was established that the optical characteristics of the studied films CdS and CdTe are insensitive to hard ultraviolet irradiation. The crystalline structure of the CdS and CdTe layers is changed after irradiation. The period of the lattice for cadmium sulfide films increases from c = 6.77(01) Å to c = 6.78(88) Å, which may be due to the formation of point defects and defective complexes. Decrease the integral FWHM of the peaks on the X-ray diffraction patterns of the layers of CdS and CdTe was observed, due to the increase of the coherent scattering regions as a result in the process of near-surface layers partial recrystallization of the investigated films.Досліджено вплив жорсткого ультрафіолетового випромінювання на кристалічну структуру, морфологію поверхні та оптичні характеристики напівпровідникових шарів CdS та CdTe, отриманих магнетронним розпиленням на постійному струмі. Встановлено, що оптичні характеристики досліджених плівок CdS та CdTe нечутливі до опромінення жорстким ультрафіолетом. Кристалічна структура шарів плівок CdS і CdTe після опромінення змінюються. Період ґратки для плівок сульфіду кадмію збільшується від с = 6,77(01) Å до с = 6,78(88) Å, що може бути пов’язано з утворенням точкових  дефектів та дефектних комплексів. В результаті опромінення жорстким ультрафіолетом спостерігається зменшення ширини піків на рентгендифрактограмах шарів CdS і CdTe, що пов’язано зі збільшенням областей когерентного розсіювання в результаті часткової рекристалізації приповерхневих шарів досліджених плівок

Ballistic versus diffusive magnetoresistance of a magnetic point contact

The quasiclassical theory of a nanosize point contacts (PC) between two ferromagnets is developed. The maximum available magnetoresistance values in PC are calculated for ballistic versus diffusive transport through the area of a contact. In the ballistic regime the magnetoresistance in excess of few hundreds percents is obtained for the iron-group ferromagnets. The necessary conditions for realization of so large magnetoresistance in PC, and the experimental results by Garcia et al are discussedComment: 4 pages, TEX, 1 Figur

Mechanisms of Spontaneous Current Generation in an Inhomogeneous d-Wave Superconductor

A boundary between two d-wave superconductors or an s-wave and a d-wave superconductor generally breaks time-reversal symmetry and can generate spontaneous currents due to proximity effect. On the other hand, surfaces and interfaces in d-wave superconductors can produce localized current-carrying states by supporting the T-breaking combination of dominant and subdominant order parameters. We investigate spontaneous currents in the presence of both mechanisms and show that at low temperature, counter-intuitively, the subdominant coupling decreases the amplitude of the spontaneous current due to proximity effect. Superscreening of spontaneous currents is demonstrated to be present in any d-d (but not s-d) junction and surface with d+id' order parameter symmetry. We show that this supercreening is the result of contributions from the local magnetic moment of the condensate to the spontaneous current.Comment: 4 pages, 5 figures, RevTe