Measurements of surface impedance of superconductors as a function of frequency in microwave range

We report measurements of the complex resistivity in YBCO and MgB$_2$ thin films over a continuous frequency spectrum in the microwave range, making use of a Corbino disk geometry. The paper mainly focuses on the extraction of the resistivity from raw data, displaying data analysis procedure and its limits of validity. We obtain and show resistivity curves as a function of frequency and temperature denoting a frequency dependent widening of the superconducting transition.Comment: 12 pages, 7 figures. Extended and revised version of cond-mat/0307143 (2003

Vortex state microwave response in superconducting cuprates and MgB2_2

We investigate the physics of the microwave response in YBa$_{2}$Cu$_{3}$O$_{7-\delta}$, SmBa$_{2}$Cu$_{3}$O$_{7-\delta}$ and MgB$_{2}$ in the vortex state. We first recall the theoretical basics of vortex-state microwave response in the London limit. We then present a wide set of measurements of the field, temperature, and frequency dependences of the vortex state microwave complex resistivity in superconducting thin films, measured by a resonant cavity and by swept-frequency Corbino disk. The combination of these techniques allows for a comprehensive description of the microwave response in the vortex state in these innovative superconductors. In all materials investigated we show that flux motion alone cannot take into account all the observed experimental features, neither in the frequency nor in the field dependence. The discrepancy can be resolved by considering the (usually neglected) contribution of quasiparticles to the response in the vortex state. The peculiar, albeit different, physics of the superconducting materials here considered, namely two-band superconductivity in MgB$_{2}$ and superconducting gap with lines of nodes in cuprates, give rise to a substantially increased contribution of quasiparticles to the field-dependent microwave response. With careful combined analysis of the data it is possible to extract or infer many interesting quantities related to the vortex state, such as the temperature-dependent characteristic vortex frequency and vortex viscosity, the field dependence of the quasiparticle density, the temperature dependence of the $\sigma$-band superfluid density in MgB$_{2}$Comment: 51 pages, 27 figures, to appear as a book chapter (Nova Science

Surface impedance of superconductive thin films as a function of frequency in microwave range

We report measurements of the complex resistivity in $YBCO$ and $MgB_2$ thin films over a continuous frequency spectrum in the microwave range, making use of a Corbino disk geometry. The paper mainly focuses on the extraction of the resistivity from raw data, displaying data analisys procedure and its limits of validity. We obtain and show resistivity curves as a function of frequency and temperature denoting a frequency dependent widening of the superconductive transition.Comment: 8 pages, Latex, 5 figure

New aspects of microwave properties of Nb in the mixed state

We present a study of the frequency dependence of the vortex dynamics in a conventional superconductor. We have employed a swept-frequency, Corbino-disk technique to investigate the temperature (3.6K-Tc) and high-field (from Hc2/2 to Hc2) microwave complex resistivity in Nb thin (20-40 nm) films as a function of the frequency (1-20 GHz). We have found several previously unnoticed features: (i) a field-dependent depinning frequency in the GHz range; (ii) deviations from the accepted frequency dependence, that can be ascribed to some kind of vortex creep; (iii) the presence of switching phenomena, reminiscent of vortex instabilities. We discuss the possible origin of the features here reported.Comment: 5 pages, 3 figures, presented at VORTEX VI Conference, to appear on Physica

Vortex state microwave resistivity in Tl-2212 thin films

We present measurements of the field induced changes in the 47 GHz complex resistivity, $\Delta \tilde \rho(H,T)$, in Tl$_{2}$Ba$_{2}$CaCu$_{2}$O$_{8+x}$ (TBCCO) thin films with $T_{c}\simeq$ 105 K, prepared on CeO$_{2}$ buffered sapphire substrates. At low fields ($\mu_{0}H<$10 mT) a very small irreversible feature is present, suggesting a little role of intergranular phenomena. Above that level $\Delta \tilde \rho(H,T)$ exhibits a superlinear dependence with the field, as opposed to the expected (at high frequencies) quasilinear behaviour. We observe a crossover between predominantly imaginary to predominantly real (dissipative) response with increasing temperature and/or field. In addition, we find the clear scaling property $\Delta \tilde \rho(H,T)=\Delta \tilde \rho[H/H^{*}(T)]$, where the scaling field $H^{*}(T)$ maps closely the melting field measured in single crystals. We discuss our microwave results in terms of loss of flux lines rigidity.Comment: 8 pages, 3 figures, proceedings of 9th HTSHFF, accepted for publication on J. Supercon

Access to work and disability: the case of Italy

This paper is an empirical study on the work opportunities of people with disability using the Istat survey on health conditions 2004-2005, that collects information on the health status and disability condition on the whole Italian population and allows a comparison between disabled and not disabled persons. For this purpose we investigate the probability to be employed by disability status. People with disability show a lower probability of being employed and their employment probability is even lower if with psychic disability. By disaggregating by disability status our analysis can recognize a higher positive effect of investing in education on the probability of employment for people with disabilities.This paper is an empirical study on the work opportunities of people with disability using the ISTAT survey on Health Conditions and Use of Health Services Survey 2004-2005, that collects information on the health status and disability condition on the whole Italian population and allows a comparison between disabled and not disabled persons. For this purpose we investigate the probability to be employed by disability status. People with disability show a lower probability of being employed, the availability of data on the type of disability allows to detect amongst disabled a lower employment probability for individuals with psychic disability. By disaggregating by disability status our analysis can recognize a higher positive effect of investing in education on the probability of employment for people with disabilities

DO CONSUMERS PERCEIVE A GREEN COUNTRY IMAGE OF A COUNTRY? ATTITUDINAL ANTECEDENTS AND IMPACT ON WILLINGNESS TO BUY

Context: Consumers are becoming increasingly concerned with sustainable issues: not only products and suppliers but even countries have started to be perceived in terms of their level of green image. This acknowledgement calls for a revision of traditional international marketing models aimed at investigating the impact of a specific country image on consumer behavior, considering also the effect of the image of sustainability possessed by that country. Purpose: This work aims to exploring the connection between the Green Country of Origin Image (GCoI) of a country and the Willingness to Buy (WTB) by the consumers of another country. This is done by assessing their Attitude Towards Green Products (GATT), considered as a mediating construct impacted by Environmental Concern (EC) and Perceived Consumer Effectiveness (PCE). Data: Primary research data were gathered through a survey based on the administration of an online questionnaire targeting a convenient sample of Indian consumers, applying structural equation modelling to assess the GCoI of Made in Italy food products. Results: Findings evidenced the goodness of the proposed model: EC and PCE are positively related with GATT, which, in turn, positively affect GCoI. Finally, GCoI has a positive and significant effect on the WTB. Originality: GCoI has been poorly investigated. This study enriches the current body of knowledge concerning country image determinants in relation to sustainable consumption, contributing to the international marketing and consumer behavior literature in a sustainable perspective. Implications: This research holds pragmatic significance for policy makers and scholars alike, and marketers striving to advocate national offerings on international markets through the added value of sustainable food perceptions and practices. It also deeps the comprehension of consumer behavior within the realm of sustainable consumption for stimulating eco-conscious decisions

Microwave properties of Nb/PdNi/Nb trilayers. Observation of flux flow in excess of Bardeen-Stephen theory

We combine wideband (1-20 GHz) Corbino disk and dielectric resonator (8.2 GHz) techniques to study the microwave properties in Nb/PdNi/Nb trilayers, grown by UHV dc magnetron sputtering, composed by Nb layers of nominal thickness $d_S$=15 nm, and a ferromagnetic PdNi layer of thickness $d_F$= 1, 2, 8 and 9 nm. We focus on the vortex state. Magnetic fields up to $H_{c2}$ were applied. The microwave resistivity at fixed $H/H_{c2}$ increases with $d_F$, eventually exceeding the Bardeen Stephen flux flow value.Comment: 6 pages. Submitted to Journal of Superconductivity and Novel Magnetis