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We propose a model of Josephson coupling between grains to explain the millimeter-wave surface impedance of oriented, polycrystalline thin films of high Tc superconductors. An effective junction IcR product and effective grain size are calculated based on recent measurements of the surface impedance. We suggest a criterion on film quality for the observation of losses intrinsic in the superconductor. The effects of crystalline orientation on surface impedance are considered.

We present experimental and theoretical results on bound states in quantum wires (narrow, twodimensional quantum channels). We study rectangular systems of constant width, varying the bend angle. This system is realized by propagation of TE-mode microwaves in flat rectangular waveguides; resonant frequencies for absorption of power are measured for various bend angles, and compared with theoretical results for bound-state (resonant) eigenvalues.

Here we report syntheses and study of composite solid polymer electrolytes (SPEs) based on a poly(ethylene glycol)-in-Li triflate material that contains an organic-inorganic composite (OIC) in which boron species are incorporated into a silica network. The structure and properties of the SPEs synthesized were characterized by scanning transmission electron microscopy (STEM), 29 Si, 11 B and 13 C solid state NMR, differential scanning calorimetry, and impedance spectroscopy. STEM allowed assessment of OIC particles in their native environment without removal of an organic component. The Lewis acid tricoordinate boron sites formed in OIC are proposed to have a stronger interaction with triflate anions than silica sites, which results in enhanced lithium ion conductivity and Li transference numbers at optimal boron concentrations. The optimum triethyl borate (TEB) concentration also leads to formation of smaller (higher surface area) OIC particles, which expose more boron sites to triflate anions. The SPE sample prepared with 10 mol% TEB exhibited a conductivity of 4.3 Â 10 À5 S cm À1 and a Li transference number of 0.89, which represents nearly single-ion conductor behaviour for the salt-in-polymer-borosilicate composite.

It has been shown that in quantum wires which contain bends there will be one or more bound states for electrons placed in such systems. Bound states have been observed in quantum wires, but detailed mapping of such states is difficult. However, there is a one-to-one correspondence between wave functions of free electrons in two-dimensional ͑2D͒ systems, and electric fields of TE modes in rectangular waveguides with the same cross section as the 2D system. We therefore construct bent waveguides, find the frequencies at which confined EM fields occur, and map out the electromagnetic energy density there. We compare the experimental results with theoretical predictions of bound state energies and eigenfunctions. The geometry has been chosen to correspond to two-dimensional systems for which quantum wire experiments have been carried out. In such systems, we can predict the number and location of the bound states in the system; in addition, we can predict the electric and magnetic fields for the confined TE modes in this system. We show very good agreement between our predictions and experiment for bent waveguides in this geometry.

Temperature (T)- and frequency (omega)-dependent conductivity measurements are reported here in amorphous niobium-silicon alloys with compositions (x) near the zero-temperature metal-insulator transition. There is a one-to-one correspondence between the frequency- and temperature-dependent conductivity on both sides of the critical concentration, thus establishing the quantum-critical nature of the transition. The analysis of the conductivity leads to a universal scaling function and establishes the critical exponents. This scaling can be described by an x-, T-, and omega-dependent characteristic length, the form of which is derived by experiment.