Showing papers by "Dave H. A. Blank published in 2002"

Magnesium-diboride ramp-type Josephson junctions

Abstract: Josephson junctions have been realized in which two superconducting magnesium-diboride (MgB2) layers are separated by a thin MgO barrier layer, using the ramp-type configuration. Their current–voltage characteristics follow the behavior described by the resistively shunted junction model, with an excess current of about 30% of the critical current Ic. A suppression of 70% of Ic was achieved in applied magnetic fields. Shapiro steps were observed by irradiating the junctions with 10.0 GHz microwaves, and the dependence of the step height on applied rf current is well described by a current–source model. Reference samples prepared without the MgO layer showed strong-link behavior with large Ic values.

Growth studies of Ba(1-x)K(x)BiO3-delta thin films by pulsed-laser deposition

Abstract: A study is presented on pulsed-laser deposition of thin films of Ba1−xKxBiO3−δ (BKBO) and its parent compound BaBiO3−δ (BBO). BKBO is a non-cuprate high-TC (30 K) superconductor with relatively long coherence length (5 nm) and shows BCS like behavior. Therefore, BKBO is an attractive candidate for superconducting electronic device applications. Furthermore, the insulator BBO is suitable as barrier material. We deposited BKBO thin films from potassium-overdoped targets (Ba0.6K0.8BiO3−δ) in order to compensate for the volatility of potassium in our efforts to obtain superconducting Ba1−xKxBiO3−δ (x=0.3–0.4) thin films. The deposition parameters and annealing procedure were optimized to achieve good quality films. Especially, the substrate temperature is important, because it influences simultaneously the content of potassium and crystallinity of the growing film. This combination hampers the optimization, because they cannot be controlled independently. Furthermore, we will present our first attempts to control the stoichiometry using intervals of different pulsed-laser repetition rates.