A Discrete Version of the Inverse Scattering Problem and the J-matrix Method

The problem of the Hamiltonian matrix in the oscillator and Laguerre basis construction from the S-matrix is treated in the context of the algebraic analogue of the Marchenko method.Comment: 11 pages. The Laguerre basis case is adde

Proximity Effect Enhancement Induced by Roughness of SN Interface

Critical temperature reduction $\Delta T_c$ is considered for a thin film of a layered superconductor (S) with a rough surface covered by a thick layer of a normal metal (N). The roughness of the SN interface increases the penetration of electrons from the normal metal into the superconductor and leads to an enhancement of the proximity effect. The value of $\Delta T_c$ induced by the roughness of the SN interface can be much higher than $\Delta T_c$ for a film with a plain surface for an extremely anisotropic layered superconductor with the coherence lengths $\xi_a,\xi_b\gg\xi_c$.Comment: 2 page

Nonlinear resonance in a three-terminal carbon nanotube resonator

The RF-response of a three-terminal carbon nanotube resonator coupled to RF-transmission lines is studied by means of perturbation theory and direct numerical integration. We find three distinct oscillatory regimes, including one regime capable of exhibiting very large hysteresis loops in the frequency response. Considering a purely capacitive transduction, we derive a set of algebraic equations which can be used to find the output power (S-parameters) for a device connected to transmission lines with characteristic impedance $Z_0$.Comment: 16 pages, 8 figure

NN potentials from inverse scattering in the J-matrix approach

An approximate inverse scattering method [7,8] has been used to construct separable potentials with the Laguerre form factors. As an application, we invert the phase shifts of proton-proton in the $^1S_0$ and $^3P_2-^3F_2$ channels and neutron-proton in the $^3S_1-^3D_1$ channel elastic scattering. In the latter case the deuteron wave function of a realistic $np$ potential was used as input.Comment: LaTex2e, 17 pages, 3 Postscript figures; corrected typo

Boundary resistance in magnetic multilayers

Quasiclassical boundary conditions for electrochemical potentials at the interface between diffusive ferromagnetic and non-magnetic metals are derived for the first time. An expression for the boundary resistance accurately accounts for the momentum conservation law as well as essential gradients of the chemical potentials. Conditions are established at which spin-asymmetry of the boundary resistance has positive or negative sign. Dependence of the spin asymmetry and the absolute value of the boundary resistance on the exchange splitting of the conduction band opens up new possibility to estimate spin polarization of the conduction band of ferromagnetic metals. Consistency of the theory is checked on existing experimental data.Comment: 8 pages, 3 figures, designed using IOPART styl

Quantum Nondemolition Measurement of Discrete Fock States of a Nanomechanical Resonator

We study theoretically a radio frequency superconducting interference device integrated with a nanomechanical resonator and an LC resonator. By applying adiabatic and rotating-wave approximations, we obtain an effective Hamiltonian that governs the dynamics of the mechanical and LC resonators. Nonlinear terms in this Hamiltonian can be exploited for performing a quantum nondemolition measurement of Fock states of the nanomechanical resonator. We address the feasibility of experimental implementation and show that the nonlinear coupling can be made sufficiently strong to allow the detection of discrete mechanical Fock states

Theory of AC Josepson Effect in Superconducting Constrictions

We have developed a microscopic theory of ac Josephson effect in short ballistic superconducting constrictions with arbitrary electron transparency and in constrictions with diffusive electron transport. The theory is valid for arbitrary miscroscopic structure of the superconducting electrodes of the constriction. As applications of the theory we study smearing of the subgap current singularities by pair-breaking effects and also the structure of these singularities in the constrictions between the composite S/N electrodes with the proximity-induced gap in the normal layer.Comment: 11 pages, RevTex, 3 figures available on reques

Depinning transition of dislocation assemblies: pileup and low-angle grain boundary

We investigate the depinning transition occurring in dislocation assemblies. In particular, we consider the cases of regularly spaced pileups and low angle grain boundaries interacting with a disordered stress landscape provided by solute atoms, or by other immobile dislocations present in non-active slip systems. Using linear elasticity, we compute the stress originated by small deformations of these assemblies and the corresponding energy cost in two and three dimensions. Contrary to the case of isolated dislocation lines, which are usually approximated as elastic strings with an effective line tension, the deformations of a dislocation assembly cannot be described by local elastic interactions with a constant tension or stiffness. A nonlocal elastic kernel results as a consequence of long range interactions between dislocations. In light of this result, we revise statistical depinning theories and find novel results for Zener pinning in grain growth. Finally, we discuss the scaling properties of the dynamics of dislocation assemblies and compare theoretical results with numerical simulations.Comment: 13 pages, 8 figure

Contributions of spontaneous phase slippage to linear and non-linear conduction near the Peierls transition in thin samples of o-TaS_3

In the Peierls state very thin samples of TaS_3 (cross-section area \sim 10^{-3} mkm^2) are found to demonstrate smearing of the I-V curves near the threshold field. With approaching the Peierls transition temperature, T_P, the smearing evolves into smooth growth of conductance from zero voltage interpreted by us as the contribution of fluctuations to the non--linear conductance. We identify independently the fluctuation contribution to the linear conductance near T_P. Both linear and non-linear contributions depend on temperature with close activation energies \sim (2 - 4) x 10^3 K and apparently reveal the same process. We reject creep of the {\it continuous} charge-density waves (CDWs) as the origin of this effect and show that it is spontaneous phase slippage that results in creep of the CDW. A model is proposed accounting for both the linear and non-linear parts of the fluctuation conduction up to T_P.Comment: 6 pages, 5 Postscript figure, RevTeX, accepted for publication in PR