The aim of this work is to investigate the potential of superconducting magnesium diboride (MgB2) thin films, prepared by the in-situ method, as broadband radiation detectors based on the microwave measurement of the complex impedance. The characterization of the films at microwave frequencies has been obtained by a coplanar resonator technique. The data analysis results in the determination of penetration depth, surface impedance and energy gap. In view of their microwave properties, particularly of the gap structure, the possible use of such MgB2 films as photon detectors is discussed in detail.

This paper reports on 4.2 GeV Au ion irradiation of YBCO coplanar resonators aimed at controlling vortex-induced microwave dissipation and nonlinearity by means of a suitable distribution of columnar defects. Two procedures were used: (1) uniform irradiation at a given dose and (ii) non-uniform irradiation, obtained by means of a moving-target technique, producing a tailored profile of columnar defect density. The last configuration is needed in order to attain an optimal compromise between defect-induced enhancement of vortex pinning and increase of dissipative scattering. The resonators were characterized before and after irradiation in order to evaluate penetration depth and surface impedance, by means of a data analysis also suitable to account for the substrate properties. It turns out that in the case of uniform irradiation the induced damage, attributed to the addition of dissipative regions, always prevails over the improvement due to vortex pinning. In contrast, in the case of the tailored dose profile, significant damage is absent, while the onset of non-linearity is shifted towards higher circulating power. The need to control vortex-induced effects is confirmed by magneto-optical analysis that puts in evidence that vortex penetration occurs even at low values of transverse dc magnetic field and temperature.

This paper reports on nonuniform heavy ion irradiations of YBCO coplanar resonators aimed at controlling vortex-induced microwave dissipation and nonlinearity. The adopted moving-target irradiation technique allows producing tailored profiles of columnar defect density to get an optimal compromise between defect-induced enhancement of vortex pinning and addition of dissipative scattering. The same samples were characterized before and after irradiation in order to evaluate the surface impedance, by means of data analysis suitable to account also for the substrate properties. In the case of the modulated dose profile, matching the fundamental-mode field distribution along the resonator, the onset of nonlinearity is shifted toward higher circulating power, without increasing dissipation. Finally, the possibility to locally modify by irradiation the properties of the material to obtain the confinement of external perturbations, while maintaining the current continuity throughout the whole device, has been preliminarily tested.

In this paper we investigate the effects of ion irradiation on the superconducting properties of polycrystalline high-density MgB2. We show that the investigated samples are quite radiation hard, both for what concerns the main reference superconducting parameters and, more important, for what concerns the details of the basic vortex dynamics. This property makes magnesium diboride a good candidate for applications in outspace and in harsh environments. The focus of the analysis is on the flux creep phenomena, studied by ac susceptibility measurements at different frequencies and applied fields. The employed analysis method allows obtaining the activation energy as a function of temperature, field and current density, in their full ranges. As a result, vortex-phase diagrams for the unirradiated and the irradiated samples can be compared and discussed.

Material aspects of heterostructural Si/CeO2, fabricated by magnetron sputtering as buffered substrates for sputtered YBa2Cu3O7-x (YBCO) films, are studied by means of X-ray diffraction, AFM, Raman and SIMS-ToF analysis. Different Si/CeO2 layouts are chosen and tri-layers Si/CeO2/YBCO, grown on the respective bi-layer substrates, are preliminary analyzed. Outstanding material issues suggest that in the framework of sputtering technology, epitaxy is out of reach for Si/CeO2/YBCO multi-layers. However, the results point toward the scalability/integrability of the technology with silicon processing when the main target consists of networking for integrated electronics.

In this paper we analyse the influence of the microwave phase noise on the Josephson junction array (JJA) reference voltage in order to investigate the limit of the contribution to the error budget of a JJA voltage standard from the microwave source.

In this paper we describe the measurement system for the 1-V Josephson voltage standard installed at IEN, which uses Josephson junction arrays, and the results that have been obtained in calibrating 1-V voltage sources so far.<>

We discuss the reproducible dependence of tunneling conductance on voltage in Nb/Bi2Sr2CaCu2O8+x (single-crystal) point-contact junctions. The large and symmetric deviations from the background conductance observed at voltages greater than the gap are interpreted in the framework of inelastic electron tunneling at the surface of the high-temperature superconductor. The peaks of the odd second derivative of the tunneling current (d(2)I/dV(2))(odd), Shifted of the sum of Nb and Bi2Sr2CaCu2O8+x energy gaps, show a good correspondence with the peaks of the generalized phonon density of states G(omega) determined from neutron-scattering data. The amplitude of the relative deviations of the conductance from the background is explained, as a first approximation, by means of inelastic tunneling at the surface of Bi2Sr2CaCU2O8+x assuming a large electron-phonon coupling strength lambda for selected phonon modes and, simultaneously, a small potential barrier U and a small thickness delta of the region where the inelastic process occurs.

We discuss the reproducible dependence of tunneling conductance on voltage in Nb/${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathit{x}}$ (single-crystal) point-contact junctions. The large and symmetric deviations from the background conductance observed at voltages greater than the gap are interpreted in the framework of inelastic electron tunneling at the surface of the high-temperature superconductor. The peaks of the odd second derivative of the tunneling current (${\mathit{d}}^{2}$I/${\mathit{dV}}^{2}$${)}_{\mathrm{odd}}$, shifted of the sum of Nb and ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathit{x}}$ energy gaps, show a good correspondence with the peaks of the generalized phonon density of states G(\ensuremath{\omega}) determined from neutron-scattering data. The amplitude of the relative deviations of the conductance from the background is explained, as a first approximation, by means of inelastic tunneling at the surface of ${\mathrm{Bi}}_{2}$${\mathrm{Sr}}_{2}$${\mathrm{CaCu}}_{2}$${\mathrm{O}}_{8+\mathit{x}}$ assuming a large electron-phonon coupling strength \ensuremath{\lambda} for selected phonon modes and, simultaneously, a small potential barrier U and a small thickness \ensuremath{\delta} of the region where the inelastic process occurs.

Abstract Among thermal detectors, bolometers have particular importance, being used to set high-frequency power standards. The characteristic of these sensors is that a metrological link can be realized between the electromagnetic power and a fundamental SI quantity, i.e., the direct current. In the microwave field, power standards are usually set in the range 1–10 mW without specific noise problems. However, if a power standard has to be realized under the 10 nW level, the classic bolometer must be replaced by devices working at cryogenic temperature, which have superior performance in terms of NEP . The aim of the paper is to describe the design of a low-level 1–10 nW power standard, in the 26.5–40 GHz (Ka) millimetre band by means of superconducting transition-edge bolometers. In fact, a classic low-temperature superconducting bolometer, realized with a properly etched Nb thin film, has been considered to be more reliable. Future developments foresee the adoption of both a high-temperature superconductor, e.g., YBCO, and a new type of thermometer based on the kinetic inductance of a superconducting thin film.

The large conductance deviations reproducibly observed in Nb/Bi2Sr2CaCu2O8+x point-contact junctions at energies greater than the gap are explained by inelastic tunneling at the surface of the superconducting electrodes, assuming a very large electron-phonon coupling strength λ for some phonon modes, a relatively small potential barrier U and a small thickness δ of the region where the inelastic tunneling process takes place.

Previous and recent results on transport properties of sintered YBCO before and after 6.5 MeV proton implantation are reported. The samples under study come from two different batches, processed by nominally identical preparation methods. For the first batch, irradiation produces enhancement of the critical current density, while for the second one an average damage is observed. An SEM analysis of two different samples shows dissimilar preirradiation grain boundary structures. We infer that these different structures are responsible for the dissimilar response to the irradiation.

High-Tc superconductors - much more than superconductors of higher Tc, A. Barone the present status and challenges of high temperature superconductivity, C. W. Chu problems of obtaining textured high-Tc superconducting materials for high current applications, V. P. Seminozhenko et al recent trends in the synthesis, optimization and characterization of layered lead and bismuth cuprates, B. Raveau et al flux lattice relaxation in YBCO and BSCCO single crystals in an extended frequency and temperatue range, V. Calzona et al flux pinning enhancement by fast neutron irradiation in YBa2Cu3O7-d single crystals, H.W. Weber magnetic shielding by high-Tc superconductors - shielding effects of YBCO cylinders, M. Itoh on the nature of grain boundaries in the high temperature superconductors, R. Gross and B. Mayer multilayer-type Josephson junctions and devices fabricated thereof, G. J. Gerritsma an interpretation of experimental data on high-Tc junctions, A. Di Chiara et al.(Part contents).

Transport properties in pellets of YBCO and BISCO are studied before and after 6.5-MeV proton implantation. The average critical current was strongly enhanced but in one case also weakened, probably due to the unfavorable interaction with the pre-irradiation defect structure. Characteristic parameters are compared and discussed.