Interlayer pairing in high temperature superconductors: effect of nonmagnetic impurities

The influence of impurity scattering is studied theoretically in a two-layer model for the high-T _c superconductor Y₁Ba₂Cu₃O_7– with intra- and inter-layer pairing. Two types of impurities are considered: (I) impurities which conserve the reflection symmetry of the two layers and (II) impurities which break it. Impurities of type (I) have no influence on the critical temperature. Type (II) impurities have strong influence onT _c as well as onH _c2 if there is a pairing interaction between carriers of different layers. The treatment of type (II) impurities is generalized to a periodic layer model appropriate for La_2–x Ba _x CuO₄. Available experiments on impurities in Y₁Ba₂Cu₃O_7– and La_2–x Ba _x CuO₄ are interpreted with our theory.     

Determination of the partial electron capture- and spontaneous-fission half-lives of254No

The isotope²⁵⁴No was produced in the fusion reaction⁴⁸Ca +²⁰⁸Pb. Using the velocity filter SHIP and radiochemical techniques it was found that the nuclide²⁵⁴No with a half-life of 55 s decays byα, EC, and spontaneous-fission. Deduced partial half-lives are (61±2) s forα-decay, (550 _?160 ⁺³⁷⁰ ) s for EC and [2.2 _?1.0 ^+2.0 ]×10⁴ s for spontaneous fission.     

Semi-insulating electrical properties of undoped inp after heat treatment in a phosphorus atmosphere

Nominally undoped InP wafers have been annealed in a phosphorus atmosphere under a pressure of about 5 bar at temperatures of 900 °C for about 80 h. It was found that the electrical properties of the samples changed considerably after this treatment. A room temperature resistivity of up to 2×10⁷cm (semi-insulating behaviour) was obtained in the bulk of the samples. The resistivity finally obtained depends on the starting carrier concentration of the untreated samples. The Hall coefficient and Hall mobility have been measured up to 600 °C. The results can be interpreted in terms of a deep electronic level (E _A=0.63 ... 0.65 eV below the conduction band). The Hall coefficient was always found to be negative resulting in a Hall mobility of 1.4 to 4.9×10³ cm²/Vs. The highest resistivity in nominally undoped bulk InP so far reported in the literature [1] was =3.6 × 10⁵cm. Therefore, this paper demonstrates for the first time that a really semi-insulating behaviour of >10⁷ cm can be achieved for bulk InP with the purity of nominally undoped material (10¹⁵ to 10¹⁶cm^–3).     

Pure-silica optical waveguides, fiber couplers, and high-aspect ratio submicrometer channels for electrokinetic separation devices

A new fabrication procedure for integration of ultraviolet transparent pure-silica planar waveguides, fiber couplers and high-aspect ratio submicrometer channels is presented. Only a single photolithographic mask step is required. The channels are 80-90 microm deep and the width can be reduced to about 0.5 microm, corresponding to a height-to-width ratio of more than 150. The core of the waveguides consists of pure silicon dioxide, which is favorable over doped silica, due to the absence of absorption centers associated with the dopants. This furthermore improves the long-term stability of the waveguides, because of an increased radiation resistance of the glass. The propagation loss decreases from 1.0 dB/cm at 200 nm to 0.2 dB/cm at 800 nm, which, to our knowledge, is the lowest propagation loss reported for integrated planar waveguides in the ultraviolet wavelength region to date. The effective optical path length is 1.2 mm for an absorbance cell with a nominal length of 1.0 mm, indicating effective suppression of stray light. The limit of detection for paracetamol when present in the entire channel network was determined to 3 microg/mL. Finally, the applicability of the fabricated devices for capillary electrophoresis was evaluated by separation of caffein, paracetamol and ketoprofone using absorbance detection at 254 nm.