Graduation date: 1996

Thesis (Ph. D.)--University of Wisconsin--Madison, 1982. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliographical references.

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Superconductivity in high magnetic fields has attracted considerable atten- tion in recent years. The topic is important both for our fundamental un- derstanding of superfluids and for numerous practical applications. In this thesis, we consider several effects originating from the interplay between the Landau level structure of the normal state quasiparticle spectrum, and the tendency of the quasiparticles to form Cooper pairs below the critical tem- perature. A formalism designed to describe extreme type-II superconductors close to the upper critical field H_c2 is developed. The theory which utilizes the selection rules coming from the symmetry properties of the vortex lattice, simplifies the algebra describing a superconductor in the mixed state signifi- cantly. We are, on the mean field level, able to include the quantizing effects of the magnetic field on the electron motion exactly. A main achievement is the exact calculation of the expansion coefficients giving the grand canonical potential of a superconductor in terms of a power series in the size of the or- der parameter. The result is an expression for the grand canonical potential in terms of a polynomial in a finite set of variables close to H_c2. Using this formalism, a theory for the experimentally observed damped de Haas-van Alphen (dHvA) oscillations in the mixed state of a 2-dimensional (2D) superconductor is presented. The theory is compared with numerical results and the agreement is found to be good. A simple physical interpreta- tion of the damping is provided. The dependence of the damping on a finite Zeeman term, temperature, and the magnetic field is considered. A compar- ison of the theory with experimental data for the quasi-2D superconductor K-(ET)₂Cu(NCS)₂ yields good agreement. The attenuation of a longitudinal sound wave in the mixed state is then calculated. In analogy with the dHvA effect, we predict that there should be damped oscillations in the sound attenuation in the mixed state as the exter- nal magnetic field is varied. Furthermore, the dependence of the oscillations on the sound frequency and temperature is shown to yield information on the low lying quasiparticle spectrum. Especially, the presense of gapless excita- tions due to the magnetic field makes the attenuation qualitatively different as compared to the attenuation in the Meissner state. Some formal convergence properties of the Gor'kov theory for type-II su- perconductors close to H_c2 are derived. We show that the theory is essentially a high temperature expansion; the convergence radius of the Gor'kov series is proportional to k_BT when there is a Landau level at the chemical potential.

Au Yeung Yue Fung. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references. / Text in English; abstracts in English and Chinese. / Au Yeung Yue Fung. / Abstract --- p.i / 論文摘要 --- p.ii / Acknowledgements --- p.iii / Table of Contents --- p.iv / List of Figures --- p.vi / List of Tables --- p.viii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- Genesis --- p.1-1 / Chapter 1.2 --- Aims and Objectives --- p.1-2 / Chapter 1.3 --- Layout of thesis --- p.1-3 / References --- p.1-4 / Chapter Chapter 2 --- Literature review / Chapter 2.1 --- Introduction to superconductor --- p.2-1 / Chapter 2.2 --- MgB2 --- p.2-3 / Chapter 2.2.1 --- Significance of MgB2 --- p.2-3 / Chapter 2.2.2 --- Structure and properties of MgB2 --- p.2-4 / Chapter 2.2.3 --- Superconducting mechanism of MgB2 --- p.2-5 / Chapter 2.2.4 --- Physical properties of boron and boride --- p.2-7 / Chapter 2.2.5 --- Physical properties of magnesium --- p.2-7 / Chapter 2.2.6 --- Formation of MgB2 --- p.2-8 / Chapter 2.2.7 --- MgB2 thin films --- p.2-9 / Chapter 2.2.7.1 --- Substrate --- p.2-11 / Chapter 2.2.7.2 --- Substrate temperature --- p.2-12 / Chapter 2.3 --- Contradictions as revealed by existing literatures --- p.2-13 / References --- p.2-14 / Chapter Chapter 3 --- Preparation and characterization of bulk MgB2 / Chapter 3.1 --- Bulk MgB2 fabrication / Chapter 3.2 --- Measurement and analysis techniques of bulk MgB2 --- p.3-4 / Chapter 3.2.1 --- XRD --- p.3-4 / Chapter 3.2.2 --- Meissner effect measurement --- p.3-5 / Chapter 3.3 --- Sintering time of MgB2 --- p.3-6 / Chapter 3.4 --- Concentration of Mg in sintering MgB2 --- p.3-8 / Chapter 3.5 --- Sintering temperature of MgB2 --- p.3-11 / Chapter 3.6 --- Thermal stability of MgB2 --- p.3-13 / Chapter 3.7 --- MgB2 in water --- p.3-17 / References --- p.3-19 / Chapter Chapter 4 --- Preparation and characterization of MgB2thin films / Chapter 4.1 --- Thin film deposition --- p.4-1 / Chapter 4.1.1 --- Facing-target sputtering (FTS) --- p.4-2 / Chapter 4.1.2 --- Vacuum system --- p.4-4 / Chapter 4.1.3 --- Asymmetric bipolar pulsed DC power source --- p.4-6 / Chapter 4.2 --- Fabrication of MgB2 targets --- p.4-10 / Chapter 4.3 --- Substrates --- p.4-11 / Chapter 4.4 --- Deposition procedure --- p.4-12 / Chapter 4.5 --- Deposition condition --- p.4-13 / Chapter 4.5.1 --- Deposition power --- p.4-15 / Chapter 4.5.2 --- Deposition pressure --- p.4-13 / Chapter 4.5.3 --- Annealing temperature --- p.4-18 / Chapter 4.5.4 --- Substrate temperature --- p.4-21 / Chapter 4.5.5 --- Conclusion --- p.4-26 / References --- p.4-29 / Chapter Chapter 5 --- Failed attempts of MgB2 films fabrication by in situ method / Chapter 5.1 --- In-situ method --- p.5-1 / Chapter 5.2 --- Additional FTS guns with Mg target --- p.5-2 / Chapter 5.3 --- Diode sputtering --- p.5-4 / Chapter 5.4 --- Co-evaporating fabrication --- p.5-6 / Chapter Chapter 6 --- Conclusion --- p.6-1

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 87-88). Also available on the Internet.

Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaves 87-88). Also available on the Internet.