Electromagnetic properties andHe+irradiation effects onYBa2

Abstract

We have analyzed the electromagnetic properties of small and long YBa 2 Cu 3 O 7Ϫx grain-boundary Josephson junctions. The Swihart velocity increases with junction width ͑w͒ while the ratio of the relative dielectric constant to the barrier thickness (/t) decreases. We found that the product wϫ/t is approximately constant. These results have been explained in the framework of the filamentary model, where the barrier can be regarded as a disordered dielectric medium with a high density of superconducting filaments. Experiments demonstrate that a controllable variation of these parameters can be achieved by helium irradiation at 80 keV. We give examples of an enhancement of weak-link properties of junctions for doses in the range of 10 13 cm Ϫ2. Raising the dose we can sweep the modification of the weak-link properties from an increase of the junction critical current of about 10% to a severe degradation of the coupling energy of the barrier, although the superconducting properties of the electrodes always worsen gradually.

Capacitance of Josephson junctions made on bicrystalline substrates of different geometries

“…However, the ratio / t is more dependent on the particular structure of the barrier, and so on the kind of bicrystalline substrate used for the fabrication of the JJs. The scaling law previously reported 17 for YBCO 24°[001] symmetric JJs are not fully verified for 45°[100] asymmetric JJs, pointing to a different kind of barrier. In this sense, in the final part of the paper we have focused on the comparative analysis of these two geometries to show that interesting information about the particular nature of the barrier can be deduced from the study of the evolution of the junction capacitance with junction resistance.…”

“…In a previous published work 17 we have deduced that the / t ϫ w product is approximately constant for a fixed thickness of 24°[001] tilt symmetric JJs. In Fig.…”

“…Previously, 17,18 we presented a study of the electromagnetic parameters of 24°[001] tilt symmetric JJs. For this geometry, we found a new scaling law that sets a constant product / t ϫ w (w is the width of the junction) for samples with the same thickness.…”

“…A barrier envisaged as a disordered dielectric medium with a high density of superconducting filaments taken into account in an inductive behavior can explain such a result. 17 Also we studied the evolution of the electromagnetic parameters when the barrier is modified by irradiation with helium at 80 keV and by annealing treatments in oxygen atmosphere. 18 In this paper we present a comparative analysis, in terms of electromagnetic parameters, of JJs fabricated using SrTiO 3 (STO) bicrystalline substrates of four different tilt geometries.…”

High-pressure reactively sputtered HfO2: Composition, morphology, and optical properties

“…Another advantage of this technique is the possibility of working with several targets, allowing the fabrication of multilayered structures or compounds. This technique has been successfully used to grow high-T c superconductor films, 11 titanium oxide ͑TiO 2 ͒ films, 12 and multilayer buffers for high-T c superconductor devices 13 using a multitarget system.…”