Vortex Dynamics in the High-temperature Superconductors YBa 2 Cu 3 O 7 and Bi 2 Sr 2 CaCu 2 O 8 + Delta in Low- and High-dissipative Transport Measurements PDF Download
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This thesis investigates phenomena of vortex dynamics in type II superconductors depending on the dimensionality of the flux-line system and the strength of the driving force. In the low dissipative regime of Bi_2Sr_2CaCu_2O_{8+delta} (BSCCO) the influence of oxygen stoichiometry on flux-line tension was examined. An entanglement crossover of the vortex system at low magnetic fields was identified and a comprehensive B-T phase diagram of solid and fluid phases derived. In YBa_2Cu_3O_7 (YBCO) extremely long (>100 mm) high-quality measurement bridges allowed to extend the electric-field window in transport measurements by up to three orders of magnitude. Complementing analyses of the data conclusively produced dynamic exponents of the glass transition z~9 considerably higher than theoretically predicted and previously reported. In high-dissipative measurements a voltage instability appearing in the current-voltage characteristics of type II superconductors was observed for the first time in BSCCO and shown to result from a Larkin-Ovchinnikov flux-flow vortex instability under the influence of quasi-particle heating. However, in an analogous investigation of YBCO the instability was found to appear only in the temperature and magnetic-field regime of the vortex-glass state. Rapid-pulse measurements fully confirmed this correlation of vortex glass and instability in YBCO and revealed a constant rise time (~æs).
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Languages : en
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This thesis investigates phenomena of vortex dynamics in type II superconductors depending on the dimensionality of the flux-line system and the strength of the driving force. In the low dissipative regime of Bi_2Sr_2CaCu_2O_{8+delta} (BSCCO) the influence of oxygen stoichiometry on flux-line tension was examined. An entanglement crossover of the vortex system at low magnetic fields was identified and a comprehensive B-T phase diagram of solid and fluid phases derived. In YBa_2Cu_3O_7 (YBCO) extremely long (>100 mm) high-quality measurement bridges allowed to extend the electric-field window in transport measurements by up to three orders of magnitude. Complementing analyses of the data conclusively produced dynamic exponents of the glass transition z~9 considerably higher than theoretically predicted and previously reported. In high-dissipative measurements a voltage instability appearing in the current-voltage characteristics of type II superconductors was observed for the first time in BSCCO and shown to result from a Larkin-Ovchinnikov flux-flow vortex instability under the influence of quasi-particle heating. However, in an analogous investigation of YBCO the instability was found to appear only in the temperature and magnetic-field regime of the vortex-glass state. Rapid-pulse measurements fully confirmed this correlation of vortex glass and instability in YBCO and revealed a constant rise time (~æs).
![Vortex Dynamics in the High-Temperature Superconductors YBa2Cu3O7 and Bi2Sr2CaCu2O8+[delta] in Low- and High-Dissipative Transport Measurement PDF](https://books.google.com/books/content/images/frontcover/QsC4AAAACAAJ?fife=w80-h100)
Author: Patrick Voss-de Haan
Publisher: Ibidem Press
ISBN: 9783898210249
Category : Science
Languages : en
Pages : 150
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Since their discovery in 1986, high-temperature superconductors (HTSC) are considered interesting physical systems as well as attractive candidates for a variety of technical applications. In both cases one of the key aspects to be understood is the mechanism of power dissipation, which depends primarily on vortex dynamics: the movement of magnetic flux lines in the superconductor when a transport current is applied. The present work studies vortex dynamics in experiments on two of the most prominent types of HTSC materials, YBa2Cu3O7 (YBCO) and Bi2Sr2CaCu2O8+d (BSCCO), in the limit of low and high current densities. Both, the applied transport current density and the dimensionality of the materials, strongly influence the dynamic response. For the low current limit in BSCCO this thesis concentrates on the influence of oxygen stoichiometry and in YBCO on a vortex glass phase, which indicates a true superconducting state with vanishing linear resistivity. In the high current limit, for the first time, a vortex instability is shown to exist in BSCCO, apparently arising from a fluid phase, while a similar phenomenon in YBCO reveals a clear correlation of the high-dissipative instability to the low-dissipative vortex glass phase. The author: A native of Hamburg, Germany, Patrick Voss-de Haan studied physics at Stanford University and the University of Mainz. After completing a degree in the area of atomic physics and laser spectroscopy he began his work in solid state physics and superconductors, from which this Ph.D. thesis was compiled.
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Category : Science
Languages : en
Pages : 768
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Author: Tiziano Teruzzi
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Languages : en
Pages : 175
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Author: Ana Mazilu
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Languages : en
Pages : 310
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Author: Heather Quantz
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Category : High temperature superconductors
Languages : en
Pages : 80
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![Studies of Vortex Dynamics in YBa[2]Cu[3]O[7-delta] in the Radio Frequency Regime PDF](https://books.google.com/books/content/images/frontcover/SDtuGwAACAAJ?fife=w80-h100)
Author: Hui Wu
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Languages : en
Pages : 232
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The equilibrium motion of vortices in two- and three-dimensional superconductors has been studied with a dc Superconducting QUantum Interference Device (SQUID). This technique has the advantage of probing the system in a non-invasive manner as well as providing dynamic information over many decades in frequency. Through measurements of the spectral density of magnetic flux noise, S[sub[Phi]]([omega]), as a function of temperature and applied magnetic field, the effects of proton and heavy ion irradiation on flux noise in crystals of YBa[sub 2]Cu[sub 3]O[sub 7[minus][delta]] have been measured and compared with the effects on the critical current, J[sub c]. Both proton and heavy ion irradiation proved effective at reducing S[sub[Phi]]([omega]), with proton irradiation having a larger effect. Measurement of S[sub[Phi]]([omega]) due to the equilibrium Kosterlitz-Thouless-Berezinskii transition in two-dimensional Josephson Junction Arrays (JJAs) was studied as a function of temperature for three different arrays and using three different sensors. S[sub[Phi]] is shown to obey dynamic scaling over as many as five decades in frequency, and estimates are made for the dynamic critical exponent z. An analytic theory for the high- and low-frequency behavior of S[sub[Phi]]([omega]) is presented and compared to the measured data, with the result that the low-frequency behavior is well described by the theory but the high-frequency behavior is not. Other theories and numerical simulations are described and compared with the data, but none are completely satisfactory. Lastly, suggestions for necessary further theoretical work and possible future experimental work are suggested.
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