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  • Articles  (13)
  • High-temperature superconductivity  (13)
  • 2010-2014
  • 1990-1994  (13)
  • 1985-1989
  • 1950-1954
  • Electrical Engineering, Measurement and Control Technology  (13)
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  • Articles  (13)
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Keywords
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Years
  • 2010-2014
  • 1990-1994  (13)
  • 1985-1989
  • 1950-1954
  • 1995-1999  (12)
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  • Electrical Engineering, Measurement and Control Technology  (13)
  • Physics  (13)
  • 1
    Electronic Resource
    Electronic Resource
    Superconducting gap in Pr x Y1−x Ba2Cu4O8 and YBa2−y Sr y Cu4O8 probed by infrared phonon self-energies (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 113-116 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; superconducting gap ; phonons ; reflectivity spectra ; alloys
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We report a reflectivity study of thez-polarized TO-phonons of Pr x Y1−x Ba2Cu4O8 and YBa2−y Sr y Cu4O8 alloys in the temperature range 10–300 K. Anomalies of the frequency and linewidth of the plane-oxygen vibration atω∼300 cm−1 due to the opening of the superconducting gap are found to occur upon crossing the superconducting transition temperatureT c . Phonon self-energy effects are strongly dependent onT c , providing evidence for a relative shift of the gap with respect to the energy of phonon.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730379
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  • 2
    Electronic Resource
    Electronic Resource
    Superconductivity at higher temperatures in the Hg-Ba-Ca-Cu-O compound system (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 1-7 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; compound synthesis ; pressure effect
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Our recent systematic examination of the pressure effect on high-temperature superconductors revealed that the highest achievable superconducting transition temperature (T c) in the layered cuprates may lie between ∼150 and ∼180 K. We propose that the newly discovered Hg-Ba-Ca-Cu-O (HBCCO) compound system may be one of the most promising candidates for such a high-T c superconductor, because of the possible large range of modulation doping associated with the linear oxygen coordination of divalent Hg in HBCCO. A record-high magnetically determined transition at 135 K with a zero resistivity at 134 K has been obtained by us in HgBa2Ca2Cu3O8+δ . TheT c of HgBa2Ca2Cu3O8+δ was found to increase continuously with pressure at an increasing rate up to ∼17 kbar without any sign of saturation. The thermo-power shows an underdoped characteristic. These observations suggest that theT c of HBCCO can be further enhanced with proper modulation doping without inducing any structural instabilities. The results together with the synthesis steps of HBCCO are summarized and discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00730358
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  • 3
    Electronic Resource
    Electronic Resource
    Microwave surface impedance of YBa2Cu3O7−x :S-wave versusD-wave pairing (1994)
    Springer
    Journal of superconductivity 7 (1994), S. 459-461 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; surface impedance ; pairing state
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The low temperature behavior of the microwave surface resistanceR s and the penetration provides information on the pairing state. Fully oxygenated films with low de-resistivity in the normal state exhibit an exponential temperature dependence corresponding to values of the energy gap up to 10 meV. For oxygen deficient films a linearR s(T) was observed, similar to single crystals. This can be explained qualitatively by induced superconductivity in the copper-oxygen chains.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00724589
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  • 4
    Electronic Resource
    Electronic Resource
    Flux-creep activation energies at the grain boundaries of Y-Ba-Cu-O superconductors in the characteristic frequency band (1993)
    Springer
    Journal of superconductivity 6 (1993), S. 243-246 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; flux pinning ; flux motion
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Measurements on the temperature and frequency dependence of the complex ac susceptibility of sintered Y1.01Ba1.95Cu2.97O x are reported. The data are used to obtain the flux-creep activation energies at the grain boundaries in the characteristic frequency band. The found nonlinear frequency dependence of these energies can be approximated differently in the low, characteristic, and high frequency bands. The relaxation frequency of thermal fluctuation of the vortex lattice (2πΓ ∼ 3×104 Hz) and the surface current density (J s=0–10 A/cm2) have been estimated.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00626264
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  • 5
    Electronic Resource
    Electronic Resource
    Microwave surface resistance of epitaxial YBa2Cu3O7 thin films at 18.7 GHz measured by a dielectric resonator technique (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 195-201 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; microwave cavities ; sample surface impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract We used a dielectric resonator technique for highly sensitive measurements of the temperature dependence of the microwave surface resistanceR s of 1×1 cm2 superconducting films at 18.7 GHz. It consists of a sapphire disc positioned on the film under investigation within a copper cavity which is acting as a radiation shield. In the TE01δ oscillation mode the highly reproducible quality factor of about 105 results in a sensitivity of ±50μΩ forR s measurements. The temperature dependence ofR s can be measured up to values as high as 1 Ω. We have investigated several YBa2Cu3O7 thin films prepared by high oxygen pressure d.c. sputtering on LaAlO3 and NdGaO3. Our best films exhibit a pronounced nonlinear behavior of the d.c. resistivityρ(T) withρ(300K)/ρ(100K) values of about 3.7. Those films show, besides the initial fall-off just belowT c , a further strong decrease ofR s at low temperatures. This was observed both at 18.7 GHz and 87 GHz, as measured by a conventional cavity end plate replacement technique. ForT≪Tc/2 these films exhibit an exp (−αT c/T) dependence ofR s withα-values around 0.4. These observations may be explained by a superconducting energy gap with 2Δ/kT c≈0.8 for charge carriers localized in the CuO chains for YBa2Cu3O7.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618067
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  • 6
    Electronic Resource
    Electronic Resource
    High-temperature superconductor antennas: Utilization of low rf losses and of nonlinear effects (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 403-416 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; antennas ; multiport antennas ; electrically small antennas ; microwave switches
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The low radio frequency (r.f.) losses in epitaxial HTS thin films allow the realization of novel antenna structures which have to be excluded in conventional antenna techniques with normal conductors because of the highly reduced radiation efficiency. Thus, the design of miniaturized but nevertheless highly efficient antennas down to a lower limit determined by both the required order of radiation pattern and the frequency bandwidth becomes possible. For a bandwidth of more than about 1%, a considerable margin for a size reduction below the “critical size” is restricted to the case of electrically small antennas and of superdirective antennas with a relatively low order of the radiation pattern, e.g. antennas with a beam of less than 15 dB maximum gain. If the size approaches the lower limit, the antennas show a sharp bandpass frequency response. This is demonstrated by means of experimental results for a novel HTS meander antenna. These bandpass characteristics can be utilized in compact multiport antenna systems in order to decouple subantennas for adjacent frequency bands. Besides the low losses in HTS's, their nonlinear properties can be used in order to realize current-controlled HTS switches for antenna systems.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618141
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  • 7
    Electronic Resource
    Electronic Resource
    A Tl-based high-temperature superconducting X-band cavity (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 431-435 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; X-band cavity ; Tl-based superconducting films ; metallic substrates
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A nonplanar X-band cavity amenable to coating with high-temperature superconducting films by conventional physical vapor deposition processes has been designed, fabricated, and tested. The cavity geometry resembles a symmetric clamshell configuration. It consists of two truncated cones joined at their bases. The specific dimensions of the cavity were calculated using the SUPERFISH computer code. Cavities were constructed using a silver-based alloy, Consil 995. The separate cavity sections were coated with Tl-based high-temperature superconducting material using a two-step deposition and annealing process. The unloaded Q values for this coated clamshell cavity are 66,000 and 105,000 at 77 and 20 K, respectively.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618144
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  • 8
    Electronic Resource
    Electronic Resource
    Advanced High-temperature superconducting components for microwave systems (1992)
    Springer
    Journal of superconductivity 5 (1992), S. 423-429 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; multiplexer ; narrow-band filter ; circulator ; high-Q spiral resonator
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The application of high-temperature superconducting thin films to microwave systems is expected to lead to major volume and weight savings as well as improved performance. To take full advantage of the properties that the new materials have to offer and justify the additional cooling equipment that accompanies the introduction of superconductivity, many HTS components will have to be integrated. In this paper some of the key microwave circuits that show great promise in this respect, such as multiplexers, circulators, and very narrowband filters, will be discussed and experimental results presented.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00618143
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  • 9
    Electronic Resource
    Electronic Resource
    A review of the linear term in the low-temperature specific heat of La2CuO4 and La2−xMxCuO4 (M = Ba, Ca, Sr) (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 201-209 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; specific heat ; lanthanum copper oxides ; linear term
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract In this report I will summarize the results of an extensive review of the low-temperature specific heat of the La-based high-temperature superconductors, withT c between 30 and 40 K, and the related nonsuperconducting compound La2CuO4. There have been two previous studies by Fisheret al. [1] and Fischeret al. [2] which also reviewed the low-temperature specific heat of these materials. This work was undertaken to extend a similar study of the 90 K superconductor YBa2Cu3O7−δ which we recently completed [3]. This review will focus exclusively on the low-temperature specific heat and will update the previous studies by including recent results.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00624509
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  • 10
    Electronic Resource
    Electronic Resource
    Microwave surface resistance and power dependence of thallium-based films deposited onto large-area silver substrates (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 261-267 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; microwave surface impedance ; Tl-based superconducting films ; metallic substrates ; field dependence of surface resistance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract Microwave surface resistance (R s ) measurements on large-area (11.4 cm2) Tl-based films deposited onto Ag (Consil 995) substrates have been made at a frequency of 18 GHz as a function of temperature. Deposition onto unoriented Ag substrates yields unoriented films characterized byR s values of 8.2 and 33.6 mΩ at 10.6 and 77 K, respectively. In contrast, similar deposition onto oriented Ag substrates yields oriented films with values of 12.6 and 14.6 mΩ at 11.2 and 77 K, respectively; corresponding Cu values are 9 and 21 mΩ. Additionally, it is found that the dependence ofR s on microwave surface magnetic fieldH s is weaker for the oriented films. These results suggest that the effect of orienting thec-axis in Tl films is twofold: (1) the high-frequency superconducting transition is made considerably sharper, resulting in a lowerR s value at 77 K, and (2) the rate of increase inR s with appliedH s is reduced. Both effects have significant ramifications for the potential application of these materials to high-frequency accelerating cavities.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625266
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  • 11
    Electronic Resource
    Electronic Resource
    RF properties of high-temperature superconductors: Cavity methods (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 297-304 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; microwave cavities ; sample surface impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A description of cavities used in the study of the microwave properties of the high-temperature superconductors is followed by a lumped-circuit analysis of the coupling of transmission lines and resonators. The frequency dependence of the reflected and transmitted microwave power and the character of transient cavity response are analyzed. Techniques are discussed for the introduction of samples of the high-temperature superconductors into microwave cavities. Following a discussion of sample surface impedance and sample geometry factor, the connection between surface resistance and cavityQ is examined as well as the connection between cavity frequency shift and surface reactance. Measurement techniques that utilize reflected or transmitted power or transient response are described.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625271
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  • 12
    Electronic Resource
    Electronic Resource
    Some potential antenna applications of high-temperature superconductors (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 287-296 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; antennas ; electrically small antennas ; antenna feed networks ; antenna arrays ; superdirectivity
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract A review of possible applications of high-temperature superconductors (HTS) to antennas and antenna feed networks is presented. The frequency range of consideration is 1 MHz to 100 GHz. Three antenna application areas seem appropriate for HTS material. (1)Electrically small antennas and their matching networks: An increase in efficiency is possible for electrically short antennas, but at the expense of bandwidth. Substantial radiated power levels (on the order of kilowatts) can be handled by the best HTS material. Substantial improvement may be realized by making only the matching network of HTS material. (2)Feed and matching networks for compact arrays with enhanced directive gain (superdirective arrays): HTS material should permit such arrays to be fabricated that have high efficiency. (3)Feed networks for millimeter-wave arrays: Low-loss feed networks using HTS microstrip transmission lines give many decibels improvement in gain.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625270
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  • 13
    Electronic Resource
    Electronic Resource
    Magnetic penetration depth measurements with the microstrip resonator technique (1990)
    Springer
    Journal of superconductivity 3 (1990), S. 311-316 
    Details
    ISSN: 1572-9605
    Keywords: High-temperature superconductivity ; magnetic penetration depth ; microwave surface impedance
    Source: Springer Online Journal Archives 1860-2000
    Topics: Electrical Engineering, Measurement and Control Technology , Physics
    Notes: Abstract The microstrip resonator technique is a convenient way to sensitively measure the temperature dependence of the magnetic penetration depth λ(T) in superconducting thin films. Because the method relies on measuring the resonant frequency of a high-Q transmission line resonator at microwave frequencies, one can very precisely measure small changes in λ(T). This technique is applied to studying the low-temperature dependence of λ(T), since that is in principle a measure of the low-lying pair-breaking excitations of the superconductor. We find that the penetration depth in niobium films is consistent with the predictions of weak coupled BCS theory. The low-temperature dependence of λ(T) inc-axis YBa2Cu3O7−δ films can be interpreted as either a weak exponential or as a power law. In addition, the measured value of λ(0) is found to be strongly dependent on the form of the temperature dependence for λ(T) used in fitting the data. Best fits over the entire temperature range are obtained with a BCS temperature dependence having values for 2Δ(0)/k BTc strictly less than 3.5, consistent with our measurements of the temperature dependence of λ(T) at low temperatures in YBa2Cu3O7−δ .
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1007/BF00625273
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