30 research outputs found
Microwave Electrodynamics of the Antiferromagnetic Superconductor GdBa_2Cu_3O_{7-\delta}
The temperature dependence of the microwave surface impedance and
conductivity are used to study the pairing symmetry and properties of cuprate
superconductors. However, the superconducting properties can be hidden by the
effects of paramagnetism and antiferromagnetic long-range order in the
cuprates. To address this issue we have investigated the microwave
electrodynamics of GdBa_2Cu_3O_{7-\delta}, a rare-earth cuprate superconductor
which shows long-range ordered antiferromagnetism below T_N=2.2 K, the Neel
temperature of the Gd ion subsystem. We measured the temperature dependence of
the surface resistance and surface reactance of c-axis oriented epitaxial thin
films at 10.4, 14.7 and 17.9 GHz with the parallel plate resonator technique
down to 1.4 K. Both the resistance and the reactance data show an unusual
upturn at low temperature and the resistance presents a strong peak around T_N
mainly due to change in magnetic permeability.Comment: M2S-HTCS-VI Conference Paper, 2 pages, 2 eps figures, using Elsevier
style espcrc2.st
Microwave Electrodynamics of Electron-Doped Cuprate Superconductors
We report microwave cavity perturbation measurements of the temperature
dependence of the penetration depth, lambda(T), and conductivity, sigma(T) of
Pr_{2-x}Ce_{x}CuO_{4-delta} (PCCO) crystals, as well as parallel-plate
resonator measurements of lambda(T) in PCCO thin films. Penetration depth
measurements are also presented for a Nd_{2-x}Ce_{x}CuO_{4-delta} (NCCO)
crystal. We find that delta-lambda(T) has a power-law behavior for T<T_c/3, and
conclude that the electron-doped cuprate superconductors have nodes in the
superconducting gap. Furthermore, using the surface impedance, we have derived
the real part of the conductivity, sigma_1(T), below T_c and found a behavior
similar to that observed in hole-doped cuprates.Comment: 4 pages, 4 figures, 1 table. Submitted to Physical Review Letters
revised version: new figures, sample characteristics added to table, general
clarification give
Coupling mechanism and microwave surface impedance of layered superconductors
Dottorato di ricerca in fisica. 11. ciclo. Advisors Luigi Maritato e Steven M. Analge. Coordinatore Gaetano ScarpettaConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal
Advances in Thin-Film Si Solar Cells by Means of SiOx Alloys
The conversion efficiency of thin-film silicon solar cells needs to be improved to be competitive with respect to other technologies. For a more efficient use of light across the solar spectrum, multi-junction architectures are being considered. Light-management considerations are also crucial in order to maximize light absorption in the active regions with a minimum of parasitic optical losses in the supportive layers. Intrinsic and doped silicon oxide alloys can be advantageously applied within thin-film Si solar cells for these purposes. Intrinsic a-SiOx:H films have been fabricated and characterized as a promising wide gap absorber for application in triple-junction solar cells. Single-junction test devices with open circuit voltage up to 950 mV and ~1 V have been demonstrated, in case of rough and flat front electrodes, respectively. Doped silicon oxide alloys with mixed-phase structure have been developed, characterized by considerably lower absorption and refractive index with respect to standard Si-based films, accompanied by electrical conductivity above 10−5 S/cm. These layers have been successfully applied both into single-junction and micromorph tandem solar cells as superior doped layers with additional functionalities
Degradation of micromorph silicon solar cells after exposure to 65 MeV protons
Silicon micromorph tandem solar cells, grown on commercial. TCO coated substrates by plasma enhanced chemical vapour deposition, with an initial efficiency higher than 10%, have been degraded, in order to check their stability under space conditions, by irradiation with 65 MeV protons with fluences ranging from 10^12 protons/cm^2 up to 10^14 protons/cm^2. For low proton fluences we find a stronger decrease of the top amorphous cell photocurrent due to the stronger impact of the proton beam on the glass substrate transparency in the visible wavelength range, as compared to the infrared range. Only for very high fluences a stronger degradation of the photocurrent in the infrared wavelength range where the bottom microcrystalline cell is dominating the spectral response, has been observed. Because the non-irradiated cell has been found to be spectrally mismatched in favour of the top amorphous cell under AM1.5 and even more under AM0 irradiation conditions, for low and intermediate fluences the irradiation decreases the spectral mismatch of the micromorph tandem cells and results consequently in a relative stabilization of the irradiation induced degradation