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Languages : en
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Ultrasonic techniques were used to characterize the properties of high Tc and other unconventional superconductors. A pontoon technique was developed to investigate thin films with surface acoustic waves SAW. A cw sampling technique was modified in order to sensitively study vortex motion in small superconducting single crystals of YBCO. The penetration field of melt textured YBCO was observed ultrasonically and analysis of the data yields the superconducting energy gap in its domain boundaries. Phase diagrams of superconducting UPt3 were determined ultrasonically. The effect of a coherence phase transition on ultrasonic attenuation in CeCu6 was measured. A theoretical model was developed to quantitatively explain the decrease in insertion loss at the superconducting transition of a SAW delay line made with YBCO interdigital electrodes. Two sets of attenuation and velocity signatures were observed in a large single crystal La(1.85)Sr(0.15)CuO4 which correspond to the superconducting transition and to a Neel transition in the superconducting state. SAW measurements using the pontoon technique on single crystals and thin films of YBCO demonstrate the importance of pinning sites in determining the nature of vortex transitions. A two dimensional theoretical model was developed for determining the acoustic radiation impedance of resonating rectangular parallelepipeds. The effect of a surrounding medium on the resonance spectra of a vibrating solid sphere was derived theoretically, and the theoretical results compare favorably with experimental data.
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Languages : en
Pages : 0
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Ultrasonic techniques were used to characterize the properties of high Tc and other unconventional superconductors. A pontoon technique was developed to investigate thin films with surface acoustic waves SAW. A cw sampling technique was modified in order to sensitively study vortex motion in small superconducting single crystals of YBCO. The penetration field of melt textured YBCO was observed ultrasonically and analysis of the data yields the superconducting energy gap in its domain boundaries. Phase diagrams of superconducting UPt3 were determined ultrasonically. The effect of a coherence phase transition on ultrasonic attenuation in CeCu6 was measured. A theoretical model was developed to quantitatively explain the decrease in insertion loss at the superconducting transition of a SAW delay line made with YBCO interdigital electrodes. Two sets of attenuation and velocity signatures were observed in a large single crystal La(1.85)Sr(0.15)CuO4 which correspond to the superconducting transition and to a Neel transition in the superconducting state. SAW measurements using the pontoon technique on single crystals and thin films of YBCO demonstrate the importance of pinning sites in determining the nature of vortex transitions. A two dimensional theoretical model was developed for determining the acoustic radiation impedance of resonating rectangular parallelepipeds. The effect of a surrounding medium on the resonance spectra of a vibrating solid sphere was derived theoretically, and the theoretical results compare favorably with experimental data.
Author: Moises Levy
Publisher: Academic Press
ISBN: 0323148549
Category : Science
Languages : en
Pages : 486
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Book Description
Physical Acoustics, Volume XX: Ultrasonics of High-Tc and Other Unconventional Superconductors covers the many acoustic studies of the high-Tc superconductors. This book is composed of 10 chapters that include some unconventional superconducting systems, such as superfluid 3He, heavy Fermion superconductors, and magnetic re-entrant superconductors. The introductory chapter summarizes the results that have been observed in Bardeen, Cooper, and Schriefer superconductors as functions both of temperature and magnetic field. The subsequent chapters deal with the theoretical and experimental aspects of ultrasonic study of some unconventional superconductors. Considerable chapters are devoted to the measurements with sound waves on the sintered high-Tc superconducting systems. These chapters examine first the temperature and magnetic field dependence of the velocity and elastic constants in sintered high-Tc superconductors, as well as the sound absorption and dispersion measurements on single crystals of these superconductors. Discussions on the small-sample resonant ultrasound technique that uses thin piezoelectric films and the effect of oxygen on superconducting properties and the response of sound to these additions are also provided in these chapters. The concluding chapter presents a theoretical foundation for sound measurements in the superconducting state, emphasizing the effects of multigap structures and gas anisotropy on sound attenuation in the superconducting state of the cuprate superconductors. This volume will be of great benefit to researchers in the fields of electronics technology and in applied and engineering mechanics.
Author: Moises Levy
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Category :
Languages : en
Pages : 8
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Ultrasonic techniques have been used to characterize properties of high T sub c and other unconventional superconductors. Attenuation and velocity measurements with shear waves have been performed on a sintered sample of HgBa2CuO4 and single crystal and melt textured samples of YBCO as a function of magnetic field. Anomalous behavior is observed which may be due to the fact that sound waves are sensitive to the total number of flux lines sampled, regardless of their orientation. A pontoon technique was used to launch surface acoustic waves SAW through a single crystal platelet of YBCO. A relative maximum in attenuation is observed at around 90K which may be associated with a relaxation process. Measurements on a SAW reflective array compressor made of superconducting YBCO appear to indicate that the YBCO reflecting chevrons are more effective in reflecting the SAW in the normal state than in the superconducting state. The insertion loss of a SAW delay line made with YBCO interdigital electrodes decreased when the electrodes became superconducting. A theoretical model has been developed to quantitatively explain these results.
Author: Moises Levy
Publisher:
ISBN:
Category :
Languages : en
Pages : 23
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The objective of this research project were to characterize high Tc superconductors and heavy Fermion superconductors with longitudinal and transverse ultrasonic waves and with surface acoustic waves. Sound attenuation measurements in sintered and sinter forged Y1Ba2Cu3O7 exhibited three maxima which appear to be produced by relaxation processes with activation energies in the range of 450 K, 1100 K, and 650 K. The high activation energy is associated with the middle attenuation maximum which appears to be isotropic and is the only one present in another 123 isomorph Er1Ba2Cu3O7. This is the energy of the virtual excitations proposed in some theoretical models that is required for the appearance of high Tc superconductivity. Sound measurements in a Tl based superconducting compound exhibited a frequency independent maximum at the superconducting transition. This appears to be the first attenuation effect that is directly produced by the superconducting transition itself. Such a peak has also been observed in Y1Ba2Cu3O7 after careful analysis of the data. These may be produced by interactions with superconducting fluctuations, enhanced by the two dimensional nature of the systems.
Author: J.J. Pouch
Publisher: Trans Tech Publications Ltd
ISBN: 3035704740
Category : Technology & Engineering
Languages : en
Pages : 710
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Book Description
This collection of papers describes the synthesis, properties, characteristics and applications of the recently discovered high-temperature superconductors. Results of research activities around the world are presented.
Author: Moises Levy
Publisher:
ISBN:
Category :
Languages : en
Pages : 11
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The objective of this research is to characterize high TC superconductors with longitudinal and transverse ultrasonic waves. Both attenuation and velocity measurements have been performed on sinter forged samples of YBa2Cu3O7, which has two CuO planes perpendicular to the c-axis per unit cell. Three elastic constants, C11, C33 and C44, out of five, for this axially symmetric sample, with 80 percent of the c-axis of platelet like crystallites aligned along the forging axis, have been determined. Three maxima in attenuation are observed at 70 K, 180 K, and 250 K when longitudinal waves are propagated perpendicular to the forging axis. Only the middle maximum is observed when either longitudinal or transverse waves propagate parallel to the forging axis or perpendicular to CuO planes. Thus, the middle maximum may be due to an isotropic interaction while the other maxima may be produced by interactions associated with distortions of the CuO planes. Frequency dependent measurements on sintered samples of YBa2Cu3O7 show that the low temperature maximum is produced by a relaxation mechanism. The activation energy of the relaxation time for this maximum is about 400 k which is near the Debye temperature of this compound. Sound measurements in a sample of Ba0.625K0.375BiO3, which has a Tc=28 k and which is postulated to be a BCS superconductor, show a maximum in attenuation around 50 K. Yttrium compound, Barium compounds, Copper oxides. (mjm).
Author:
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Category :
Languages : en
Pages :
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Author: Jeong Seog Kim
Publisher:
ISBN:
Category : Superconductors
Languages : en
Pages : 334
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Author: WISCONSIN UNIV-MILWAUKEE DEPT OF PHYSICS.
Publisher:
ISBN:
Category :
Languages : en
Pages : 20
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High Tc superconducting controlling elements for frequency tunable surface acoustic wave SAW filters and dispersion lines in the 0.5 to 4 GHz range have been proposed and designed. Ultrasonic attenuation and velocity measurements in sinter forged YBa2Cu3O7 indicate that the sound waves are interacting with excitations which are confined to the CuO planes. Proximity SAW coupling to a two-dimensional electron gas 2 DEG has placed limits on the localization lengths of the 2 DEG. A new phase transition has been ultrasonically discovered in the mixed state of the heavy Fermion superconductor UPt3. An anomalous increase in attenuation in the superconducting state of the reentrant superconductor system Er(1-x)Ho(x)Rh(4)B4 implies a novel interaction mechanism in this system. SAW measurements on granular superconducting films demonstrate that SAW measure the sheet resistivity of these films on a length scale comparable to the SAW wavelength. Keywords: Superconductors; Surface acoustic waves; Electron gas; Heavy fermion superconductors; Reentrant superconductors; Granular superconducting film. (jhd).
Author: Timothy Alan Mahl
Publisher:
ISBN:
Category :
Languages : en
Pages : 186
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