Thesis (Elec.E)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 1982. / MICROFICHE COPY AVAILABLE IN ARCHIVES AND ENGINEERING. / Bibliography: leaves 172-176. / by Chon Meng Wong. / Elec.E

For the study of cobalt oxide materials, we investigate the spin susceptibility behavior when the temperature and interaction strength vary in the whole filling region, on a triangular lattice. We find the high density of state (DOS) around the van Hove singularity point is important to the existence of a certain itinerant ferromagnetic short-range correlation. Also we study different spin singlet and triplet pairing channels in this region, and find the triplet channels especially the f-wave pairing susceptibility presents the quickest growth via the lowing of temperature. However, it is subtle to stabilize the f-wave pairing since the effective pairing interaction was found to be very small. / In the last part we discuss a special case in quantum phase transition, in which the Green's function of the system can be analytically obtained. We study the entanglement of the system to identify the quantum phase transition in the system. / We investigate several novel strong correlated phenomena in the geometrically frustrated system in this thesis. On a parallel computational grid, we do the state-of-the-art quantum Monte Carlo (QMC) numerical simulation to the extended single-band Hubbard model. We observe a wide range of measurements to clarify and demonstrate the system properties in different electron density, temperature, interaction strength. The results of the single-band Hubbard model on the triangular lattice can help us understand the magnetic property and superconductivity of the cobalt oxide materials. The results of the attractive Hubbard model on the honeycomb lattice can be used to discuss some properties of the "Bardeen-Cooper-Schrieffer (BCS) state to Bose-Einstein condensation (BEC) crossover" picture, such as Dirac Fermions' behaviors and the coexistence of fermionic and bosonic degrees of freedom in the system. / We study the BCS-BEC picture of high Tc superconductor systems. On a honeycomb lattice, we measure a wide range of observables, such as double occupancy, uniform spin susceptibility, on site pair correlation vertex, on-site pair correlation length, potential energy, kinetic energy, to monitor the BEC-type and BCS-type behaviors coexisting in the system. In different regions of the interaction strength-temperature parametric plane, we find that the BEC-type and BCS-type behaviors dominate at different regions of the interaction strength-temperature parametric plane, and they have crossover in the intermediate interaction strength region. / Su, Shiquan. / Adviser: Hai-Qing Lin. / Source: Dissertation Abstracts International, Volume: 70-06, Section: B, page: 3570. / Thesis (Ph.D.)--Chinese University of Hong Kong, 2008. / Includes bibliographical references (leaves 101-107). / Electronic reproduction. Hong Kong : Chinese University of Hong Kong, [2012] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Electronic reproduction. [Ann Arbor, MI] : ProQuest Information and Learning, [200-] System requirements: Adobe Acrobat Reader. Available via World Wide Web. / Abstracts in English and Chinese. / School code: 1307. / Su, Shiquan.

A variety of techniques are available to enable the fabrication of photonic crystal structures. Multi-beam-interference lithography (MBIL) is a relatively new technique which offers many advantages over more traditional means of fabrication. Unlike the more common fabrication methods such as optical and electron-beam lithography, MBIL is a method that can produce both two- and three-dimensional large-area photonic crystal structures for use in the infrared and visible light regimes. While multi-beam-interference lithography represents a promising methodology for the fabrication of PC structures, there has been an incomplete understanding of MBIL itself. The research in this thesis focuses on providing a more complete, systematic description of MBIL in order to demonstrate its full capabilities. Analysis of both three- and four-beam interference is investigated and described in terms of contrast and crystallography. The concept of a condition for primitive-lattice-vector-direction equal contrasts} is introduced in this thesis. These conditions are developed as nonlinear constraints when optimizing absolute contrast for producing lithographically useful interference patterns (meaning high contrast and localized intensity extrema). By understanding the richness of possibilities within MBIL, a number of useful interference patterns are found that can be created in a straightforward manner. These patterns can be both lithographically useful and structurally useful (providing interference contours that can define wide-bandgap photonic crystals). Included within this investigation are theoretical calculations of band structures for photonic crystals that are fabricatable through MBIL. The resulting calculations show that not only do most MBIL-defined structures exhibit similar performance characteristics compared to conventionally designed photonic crystal structures, but in some cases MBIL-defined structures show a significant increase in bandgap size. Using the results from this analysis, a number of hexagonal photonic crystals are fabricated using a variety of process conditions. It is shown that both rod- and hole-type photonic crystal structures can be fabricated using processes based on both positive and negative photoresist. The "light-field" and "dark-field" interference patterns used to define the hexagonal photonic crystal structures are quickly interchanged by the proper adjustment of each beam's intensity and polarization. The resulting structures, including a large area (~1 cm², 1 x 10⁹ lattice points) photonic crystal are imaged using a scanning electron microscope. Multi-beam-interference lithography provides an enabling initial step for the wafer-scale, cost-effective integration of the impressive PC-based devices into manufacturable DIPCS. While multi-beam-interference lithography represents a promising methodology for the fabrication of PC structures, it lacks in the ability to produce PC-based integrated photonic circuits. Future research will target the lack of a large-scale, cost-effective fabrication methodology for photonic crystal devices. By utilizing diffractive elements, a photo-mask will be able to combine both MBIL and conventional lithography techniques into a single fabrication technology while taking advantage of the inherent positive attributes of both.

No description available.

This thesis presents the results from Monte Carlo calculations on classical vector spins in face-centered-cubic (FCC) lattices. The goal of the study was to understand the effect of interlayer coupling, dilution of magnetic atoms in the lattice, and symmetry-changing strain. Experimental work by T. M. Giebultowicz et al. and J. A. Borchers et al. greatly inspired my work [1, 2]. J. A. Borchers's group studied NiO/CoO superlattices and observed that the magnetic order of CoO persisted above its Neel temperature due to the effect of interlayer coupling with NiO, which has a higher Neel temperature than CoO [1]. Simulating on a model of NiO/CoO bilayer reproduced the experimental results from Borchers et al. [1]. I concluded that exchange pinning on the NiO/CoO interface preserves the magnetic order of CoO above its Neel temperature significantly. Building on this initial result, a ferromagnet/antiferromagnet/ferromagnet (FM/AFM/FM) trilayer model was studied, where the ferromagnetic (FM) layers were antiferromagnetically coupled. First, I calculated the strength of the AF coupling as a function of the number of antiferromagnetic (AFM) spacer monolayers and concluded that the strength of AFM coupling decreases as the number of AFM spacer monolayers increases. Secondly, I added a uniaxial anisotropy to the model and obtained magnetization curves which exhibited hysteresis-like features with an external field and a first order magnetic transition. Lastly, I diluted the AFM spacer layer in the FM/AFM/FM trilayer by replacing magnetic spins with zero spins in the model. The dilution of AFM spacer layer caused fluctuations in the magnetization curves with external field but the strength of AFM coupling decreases as the number of AFM monolayers increases as in the nondiluted cases. The experimental results from T.M. Giebultowicz's group on MnSe/ZnTe superlattices by neutron scattering showed incommensurate helical spin order in MnSe, where MnSe layers were under tensile strain due to a small mismatching in the lattice parameter [2]. In addition, they observed that the pitch of the spin helix increased as the temperature increased [2]. I modeled the MnSe/ ZnTe system with Monte Carlo method and found that the pitch of the spin helix increased with temperature. In fact, the dependence of helix pitch on temperature was present regardless of the thickness of the sample, so I concluded that this pitch increase is not from the weakening of coupling of surface spins / Graduation date: 2013 / Access restricted to the OSU Community at author's request from Jan. 18, 2013 - July 18, 2013

Structures as determined by single crystal X-ray methods for lanthanoid(III) compounds for series of simple homoleptic species with diverse ligands frequently display variations entailing a diminution in coordination number (‘C.N.’), a consequence of the variation in the size of the atoms/ions due to the ‘lanthanoid contraction’. A change from C.N. nine to eight is common, clearly separating compounds of the light/‘early’ or heavy/‘later’ metal atoms. Earlier work on the complexes of the lanthanoid(III) picrates arose out of the exploration of simple reagents which might usefully exploit lanthanoid ion properties for purposes such as solvent extraction. They are also of potential synthetic utility because of their relatively high solubility in apolar solvents. This thesis encompasses a systematic structural study of hydrated lanthanoid picrate complexes (including those of yttrium) with a selection of dipolar aprotic solvent ligands, namely trimethylphosphate (‘tmp’), dimethylsulfoxide (‘dmso’), hexamethylphosphoramide (‘hmpa’), N,N´-dimethylacetamide (‘dma’), N-methylpyrrolidinone (‘nmp’) and octamethylpyrophosphoramide (‘ompa’), all liquids at room temperature and all unidentate, with the exception of ompa which can be considered in some cases to behave as the equivalent of two unidentate ligands, in others as a chelate. Structures of adducts of these ligands with scandium picrate are also included in order to gain further insight into the coordination behavior of the totality of the group ‘3’ transition metals, and, for similar reasons, a study of the structures of complexes of Eu(dipivaloylmethanide)3 with the same (solvent) ligands as a ‘baseline’. In the course of these studies, hydrolysis of the aprotic solvent trimethylphosphate was found to lead to novel adducts of the dimethylphosphate (‘dmp’) ligand; the introduction of polycyclic aromatic nitrogen base ligand complexes resulted in further novel mixed ligand compounds, supplemented by a study of protonated base picrate salts. This work aims not only to establish structural ‘domains of existence’ with a concomitant consideration of the associated stereochemistry for these related series of rare earth complexes, but, also, to enhance our understanding of metal ion solvation and the interactions of aromatic groups within these types of crystal structures.

Thesis (Ph.D)--Physics, Georgia Institute of Technology, 2009. / Committee Co-Chair: Conrad, Edward; Committee Co-Chair: First, Phillip; Committee Member: Carter, Brent; Committee Member: de Heer, Walter; Committee Member: Zangwill, Andrew. Part of the SMARTech Electronic Thesis and Dissertation Collection.

Thesis (Ph. D.)--University of Wisconsin--Madison, 1969. / Typescript. Vita. eContent provider-neutral record in process. Description based on print version record. Includes bibliography.

Thesis (Ph. D.)--Ohio State University, 2007. / Title from first page of PDF file. Includes bibliographical references (p. 178-188).

The polaron problem is studied, on an infinite lattice, using the continuous-time path-integral quantum Monte Carlo scheme The method is based on the Feynman technique to analytically integrate out the phonon degrees of freedom. The transformed problem is that of a single electron with retarded self-interaction in imaginary time. The Metropolis algorithm is used to sample an ensemble of electron trajectories with twisted (rather than periodic) boundary conditions in imaginary time, which allows dynamic properties of the system to by measured directly. The method is numerically "exact", in the sense that there are no systematic errors due to finite system size, trotter decomposition or finite temperature The implementation of the algorithm in continuous imaginary time dramatically increases computational efficiency compared with the traditional discrete imaginary time algorithms.