Thesis (Ph. D.)--University of Missouri-Columbia, 2003. / Typescript. Vita. Includes bibliographical references (leaf 137). Also available on the Internet.

The properties of sputter-deposited multilayered superconductors have been studied, including Mo/Ta metallic superlattices and thin films of YBa₂Cu₃O₇₋ₓ. The former have been prepared with the same integer number of atomic planes of Mo and Ta modulating the layered composition. In contrast to behavior observed in other metal-metal superlattices, Mo/Ta exhibits long range structural coherence and metallic resistivity behavior over the entire range of wavelengths down to the monolayer limit. The structural properties of these superlattices are used to explain an anomalous decrease in the c₄₄ elastic stiffness constant previously observed in Mo/Ta for 20 Å ≤ Λ ≤ 50 Å. Superconductivity measurements indicate "universal" T(c) versus ρ behavior in Mo/Ta, and tunneling results show that these superlattices are weakly-coupled BCS superconductors. The second part of this dissertation examines the properties of superconducting thin films of YBa₂Cu₃O₇₋ₓ prepared by dc triode sputtering from metallic targets of Y and Ba₂Cu₃. Post-depression annealing in O₂ is necessary to form the superconducting oxide. Various substrates were used, including sapphire and MgO, both with and without buffer layers of Ag, and SrTiO₃. The buffer layers are used to decrease the interaction of the substrate with the film. The best results occur with films deposited on MgO with a Ag buffer layer, exhibiting T(c) onsets as high as 90 K and zero resistance by 60 K. I find that the crystalline orientation of films deposited on (100) SrTiO₃ are influenced by the substrate, and re-annealing a sample can sometimes improve its superconducting properties. Overall, reproducibility is the biggest problem with this technique, as Ba metal is highly reactive with the environment.

by Tsoi Hing Lun. / Thesis (M.Phil.)--Chinese University of Hong Kong, 2002. / Includes bibliographical references (leaves 98-102). / Abstracts in English and Chinese. / Acknowledgement --- p.i / 摘要 --- p.ii / Abstract --- p.iii / Chapter Chapter 1 --- Introduction / Chapter 1.1 --- General review --- p.1 / Chapter 1.2 --- Our work --- p.4 / Chapter Chapter 2 --- Experimental setup and procedures / Chapter 2.1 --- Sample preparation --- p.6 / Chapter 2.1.1 --- ZnSe heterostructure --- p.6 / Chapter 2.1.2 --- Quantum dot --- p.7 / Chapter 2.2 --- Common aspects of Raman scattering --- p.8 / Chapter 2.3 --- General studies --- p.11 / Chapter 2.3.1 --- Excitation power density dependent studies --- p.11 / Chapter 2.3.2 --- Angular dependent studies --- p.12 / Chapter 2.3.3 --- Excitation energy dependent studies --- p.14 / Chapter 2.4 --- Peripheral measurements --- p.16 / Chapter 2.4.1 --- Spectral calibration --- p.16 / Chapter 2.4.2 --- Alignment and system stability checks --- p.18 / Chapter 2.5 --- The method of measuring the Raman scattering efficiency --- p.19 / Chapter Chapter 3 --- Band Bending at the interface of ZnSe/GaAs / Chapter 3.1 --- Results and discussions --- p.27 / Chapter Chapter 4 --- Characteristics of QD phonons / Chapter 4.1 --- Angular dependent studies --- p.38 / Chapter 4.2 --- Excitation energy dependent studies --- p.60 / Chapter 4.3 --- The nature of the QD phonons --- p.64 / Chapter 4.4 --- The measurement of the Raman scattering efficiency of QDs --- p.67 / Conclusions --- p.75 / Future work --- p.73 / Appendix1 --- p.79 / Appendix2 --- p.82 / Appendix3 --- p.86 / Appendix4 --- p.88 / Appendix5 --- p.95 / References --- p.93

Neutron diffraction experiments on europium telluride/lead telluride super-lattice systems reveal pronounced correlations between the antiferromagnetic EuTe layers. The results from an assortment of varying experimental conditions (applied magnetic field, temperature, etc.) and their relevance to the physical mechanism underlying this striking phenomena are discussed. Stochastic computer simulations are compared to this real data to examine the effects of varying the neutron coherence length and the amount of correlations in the model sample. There are rising theoretical efforts to determine the physical mechanism causing the observed correlations and a laconic overview of current theories in interlayer coupling is given herein. The investigated structures do not exhibit perfect correlations between the magnetic layers but most samples clearly show correlation effects. The description of these partial correlations, characterized by an order parameter p, is examined and a straightforward method for determining p is derived. / Graduation date: 1998

Thesis (Ph. D.)--Ohio University, November, 1991. / Title from PDF t.p.

Thesis (Ph. D. in Physics)--Vanderbilt University, Dec. 2009. / Title from title screen. Includes bibliographical references.

Thesis (M. Phil.)--Hong Kong University of Science and Technology, 2002. / Includes bibliographical references (leaves 91-97). Also available in electronic version. Access restricted to campus users.

Thesis (Ph.D.)--Hong Kong University of Science and Technology, 2006. / Includes bibliographical references. Also available in electronic version.

In this thesis, three primary findings are presented concernmg optolelectronic properties of AlGaN superlattices. First, we obtain the lowest lateral p-type resistivity and highest lateral p-type mobility to date in the AlGaN material system. Second, we obtain the first experimental results of multi-subband photoluminescence in p-type AlGaN superlattices. Last, we report the first direct measurement of perpendicular electrical transport ( electrical transport perpendicular to the superlattice planes) in AlGaN superlattices. Our research into resistivity and mobility of AlGaN superlattices stems from the fact that p-type AlGaN is highly resistive. To overcome the problem of highly resistive p-type AlGaN, we propose and demonstrate modulation doping in p-type AlGa superlattices. Our measurements yield a low-temperature lateral resistivity and mobility of 0.068 S1 • cm and 36 cm 2 /(V • s), respectively. This is the lowest resistivity and highest mobility recorded to date in p-type AlGaN and results from reduced ionized impurity scattering inherent in modulation doping. The optical properties of AlGaN superlattices are of great interest because they are often used in light-emitting diodes and laser diodes. Specifically, the absorption edge in AlGaN superlattices is typically thought of as being severely red-shifted due to internal electric fields present in AlGaN-based materials. We obtain experimental photoluminescence results on large-period superlattices that indicate that the redshifting of the absorption edge is much less than previously thought due to the combined effects of band-filling and oscillator strength on energy. We develop a computer model based on the self-consistent solution of the Poisson and Schrodinger system of equations. Our model predicts a drastic decrease in spontaneous recombination lifetime with increased transition energy, which is consistent with our experimental data. The perpendicular resistivity of AlGaN superlattices is also of critical importance to the development of AlGaN-based devices. We therefore measured the perpendicular resistivity of an n-type AlGaN superlattice and compared it to bulk n-type GaN. The superlattice has a perpendicular resistivity of 1.2 D • cm while bulk n-type GaN is 0.18 D • cm. We develop a theoretical model based on sequential tunneling and enhanced free carrier concentration to explain our experimental findings. Our model shows that perpendicular resistivity is dominated by two factors; carrier concentration and tunneling probability.

Optical lattices make it possible to trap and coherently control large ensembles of ultracold atoms. They provide the possibility to create lattice potentials that mimic the structure of solid-state systems, and to control these potentials dynamically. In this thesis, we study how dynamical manipulations of the lattice geometry can be used to perform different tasks, ranging from quantum information processing to the creation of diatomic molecules. We first examine the dynamical properties of ultracold atoms trapped in a lattice whose periodicity is dynamically doubled. We derive a model describing the dynamics of the atoms during this process, and compute the different interaction parameters of this model. We investigate different ways of using this lattice manipulation to optimise the initialisation time of a Mott-insulating state with one atom per site, and provide a scaling law related to the interaction parameters of the system. We go on to show that entangling operations between the spin of adjacent atoms are realisable with optical lattices forming arrays of double-well potentials. We study the creation of a lattice containing a spin-encoded Bell-pair in each double-well, and show that resilient, highly-entangled many-body states are realisable using lattice manipulations. We show that the creation of cluster-like states encoded on Bell-pairs can be achieved using these systems, and we provide measurement networks that allow the execution of quantum algorithms while maintaining intact the resilience of the system. Finally, we investigate the possibility to create a diatomic molecular state and simulate Fermi systems via the excitation to Rydberg levels of ground-state atoms trapped in optical lattices. We develop a method based on symbolical manipulations to compute the interaction parameters between highly-excited electrons, and evaluate them for different electronic configurations. We use these parameters to investigate the existence of diatomic molecular states with equilibrium distances comparable to typical lattice spacings. Considering the possibility to excite atoms trapped in an optical lattice to Rydberg levels such that the electronic cloud of neighbouring atoms overlap, we propose a model describing their interactions and compute its parameters. If such systems were realised, they would allow the simulation of Fermi systems at a temperature much below the Fermi temperature, thus enabling the observation of quantum phenomena hitherto inaccessible with current technology.