Charge imbalance and Josephson effects in superconductor-normal metal mesoscopic structures

We consider a $SBS$ Josephson junction the superconducting electrodes $S$ of which are in contact with normal metal reservoirs ($B$ means a barrier). For temperatures near $T_{c}$ we calculate an effective critical current $I_{c}^{\ast}$ and the resistance of the system at the currents $I<$ $I_{c}^{\ast}$ and $I>>I_{c}^{\ast}$. It is found that the charge imbalance, which arises due to injection of quasiparticles from the $N$ reservoirs into the $S$ wire, affects essentially the characteristics of the structure. The effective critical current $I_{c}^{\ast}$ is always larger than the critical current $I_{c}$ in the absence of the normal reservoirs and increases with decreasing the ratio of the length of the $S$ wire $2L$ to the charge imbalance relaxation length $l_{Q}$. It is shown that a series of peaks arises on the $I-V$ characteristics due to excitation of the Carlson-Goldman collective modes. We find the position of Shapiro steps which deviates from that given by the Josephson relation.Comment: 12 pages, 4 figures; accepted for publication in Phys. Rev.

Character of electron reflection at a normal metal-Peierls semiconductor boundary

The reflection of electrons incident from a normal metal on the boundary of the metal with a quasi-one-dimensional conductor containing a charge-density wave (CDW) is investigated theoretically. It is shown that the reflection is not of an Andreev character, as it was suggested earlier, but rather of a Bragg character. This is due to the fact that the CDW is actually an electronic crystal, and its wave vector is a reciprocal lattice vector of the electronic crystal. The ratio of the intensities of the standard and Bragg reflection depends on the phase of the CDW.Comment: 9 pages, no figures, revte

Intrinsic Josephson Effect and Violation of the Josephson Relation in Layered Superconductors

Equations describing the resistive state of a layered superconductor with anisotropic pairing are derived. The similarity with a stack of Josephson junctions is found at small voltages only, when current density in the direction perpendicular to the layers can be interpreted as a sum of the Josephson superconducting, the Ohmic dissipative and the interference currents. In the spatially uniform state differential conductivity at higher voltages becomes negative. Nonuniformity of the current distribution generates the branch imbalance and violates the Josephson relation between frequency and voltage.Comment: 11 pages, no figures, revtex, to be published in Phys. Rev. Let

On Effect of Equilibrium Fluctuations on Superfluid Density in Layered Superconductors

We calculate suppression of inter- and intralayer superconducting currents due to equilibrium phase fluctuations and find that, in contrast to a recent prediction, the effect of thermal fluctuations cannot account for linear temperature dependence of the superfluid density in high-Tc superconductors at low temperatures. Quantum fluctuations are found to dominate over thermal fluctuations at low temperatures due to hardening of their spectrum caused by the Josephson plasma resonance. Near Tc sizeable thermal fluctuations are found to suppress the critical current in the stack direction stronger, than in the direction along the layers. Fluctuations of quasiparticle branch imbalance make the spectral density of voltage fluctuations at small frequencies non zero, in contrast to what may be expected from a naive interpretation of Nyquist formula.Comment: 5 pages, LaTeX, RevTeX, Submitted to PR

Convective Term and Transversely Driven Charge-Density Waves

We derive the convective terms in the damping which determine the structure of the moving charge-density wave (CDW), and study the effect of a current flowing transverse to conducting chains on the CDW dynamics along the chains. In contrast to a recent prediction we find that the effect is orders of magnitude smaller, and that contributions from transverse currents of electron- and hole-like quasiparticles to the force exerted on the CDW along the chains act in the opposite directions. We discuss recent experimental verification of the effect and demonstrate experimentally that geometry effects might mimic the transverse current effect.Comment: RevTeX, 9 pages, 1 figure, accepted for publications in PR

Linear response and collective oscillations in superconductors with d-wave pairing

Simple and physically transparent equations for the linear response of layered superconductors with d-wave symmetry of the order parameter are derived by means of the quasiclassic kinetic theory of superconductivity. Responses to solenoidal and potential electric fields have different frequency dependencies. The conductivity describing the response to the solenoidal field is limited by the momentum relaxation, like in a normal metal. The response to the potential electric field depends, in addition, on the branch imbalance relaxation rate. The damping of plasma oscillations of superconducting electrons is determined by dielectric relaxation and is small. Relaxation of branch imbalance determined by elastic scattering is large enough to make the Carlson-Goldman mode in d-wave superconductors overdamped.Comment: 11 pages, latex, no figures, submitted to Physical Review

High-frequency oscillations in low-dimensional conductors and semiconductor superlattices induced by current in stack direction

A narrow energy band of the electronic spectrum in some direction in low-dimensional crystals may lead to a negative differential conductance and N-shaped I-V curve that results in an instability of the uniform stationary state. A well-known stable solution for such a system is a state with electric field domain. We have found a uniform stable solution in the region of negative differential conductance. This solution describes uniform high-frequency voltage oscillations. Frequency of the oscillation is determined by antenna properties of the system. The results are applicable also to semiconductor superlattices.Comment: 8 pages, 3 figure

Dissociation of vortex stacks into fractional-flux vortices

We discuss the zero field superconducting phase transition in a finite system of magnetically coupled superconducting layers. Transverse screening is modified by the presence of other layers resulting in topological excitations with fractional flux. Vortex stacks trapping a full flux and present at any finite temperature undergo an evaporation transition which corresponds to the depairing of fractional-flux vortices in individual layers. We propose an experiment with a bi-layer system allowing us to identify the dissociation of bound vortex molecules.Comment: 4 pages, 1 figure; revised version, to appear in Phys. Rev. Let