We investigate various fundamental aspects of the metal insulator transition (MIT) by employing several theoretical approaches. Describing the novel features of interacting electronic systems remains one of the principle challenges to theoretical condensed matter physics. Therefore, any effort to provide a deep insight into understanding the nature of MITs opens a new avenue for development of modern technology. First, we present a complete analytical and numerical solution of the Typical Medium Theory (TMT) for the metal-insulator transition. In this theory, we self-consistently calculate the typical amplitude of the electron wave-functions, representing the conceptually simplest order-parameter for the Anderson transition. We classify all possible universality classes for the critical behavior, that can be found within such a mean-field approach. This provides insights into how interaction-induced renormalizations of the disorder potential may produce qualitative modifications of critical behavior. We also formulate a simple description of the leading critical behavior of varies quantities, and then obtain an effective Landau theory for Anderson localization. We also develop an efficient numerical algorithm, "Cluster Typical Medium Theory" (CTMT) to capture both non-local effects and localization in disordered electronic systems. Our formalism utilizes the momentum-resolved typical density of states to characterize the localization transition. We apply this approach to the Anderson model of localization in one and two-dimensions. In one dimension, we find that the critical disorder strength scales inversely with the linear cluster size with a power-law, W[subscript c] ∼ (1/L[subscript c])[superscript 1/v]; whereas in two dimensions, the critical disorder strength decreases logarithmically with the linear cluster size. Our results are in agreement with the one-parameter scaling theory. Furthermore, we show how spatial correlations can also be captured analytically within such a self-consistent theory, by utilizing the standard Landau method of allowing for (slow) spatial fluctuations of the order parameter, and performing an appropriate gradient expansion. Our theoretical results provide insight into recent STM experiments, which were used to visualize the spatially fluctuating electronic wave functions near the metal insulator transition in Ga[subscript 1-x]Mn[subscript x]As.$ We show that, within our theory, all features of the experiment can be accounted for by considering a model of disorder renormalized by long-range Coulomb interactions. This includes the pseudogap formation, the C(R) ∼ 1/R form of the LDOS autocorrelations function, and the ζ ∼ 1/E energy dependence of the correlation length at criticality. In the second part of my Thesis, we show that introducing long-range Coulomb interactions immediately lifts the massive ground state degeneracy induced by geometric frustration for electrons on quarter-filled triangular lattices in the classical limit. Important consequences include the stabilization of a stripe-ordered crystalline (global) ground state, but also the emergence of very many low-lying metastable states with amorphous "stripe-glass" spatial structures. Melting of the stripe order thus leads to a frustrated Coulomb liquid at intermediate temperatures, showing remarkably slow (viscous) dynamics, with very long relaxation times growing in Arrhenius fashion upon cooling, as typical of strong glass formers. On shorter time scales, the system falls out of equilibrium and displays the aging phenomena characteristic of supercooled liquids above the glass transition. Our results show remarkable similarity with the recent observations of charge-glass behavior in ultra-clean triangular organic materials of the θ-(BEDT-TTF)₂ family. / A Dissertation submitted to the Department of Physics in partial fulfillment of the requirements for the degree of Doctor of Philosophy. / Fall Semester 2015. / July 10, 2015. / Anderson model, Coulomb interaction, Frustration, Glassy features, Metal-Insulator transition / Includes bibliographical references. / Vladimir Dobrosavljević, Professor Directing Dissertation; Naresh Dalal, University Representative; Luis Balicas, Committee Member; Efstratios Manousakis, Committee Member; Simon Capstick, Committee Member.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1927. / by Georges H. J. E. Lemaitre. / Ph.D.

Massachusetts Institute of Technology. Dept. of Physics. Thesis. 1973. Ph.D. / MICROFICHE COPY ALSO AVAILABLE IN SCIENCE LIBRARY. / Vita. / Includes bibliographical references. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1997. / Includes bibliographical references (p. 106-108). / by Rennan Bar-Kana. / Ph.D.

Thesis (S.B.)--Massachusetts Institute of Technology, Dept. of Physics, 2011. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 61-63). / Graphene, a newly discovered material. has been the subject of much experimental and theoretical study due to its unique electronic behavior. In this thesis, I present, my work with graduate student Joel Wang to design and fabricate Josephson junctions on high quality graphene samples. Using niobium, with its high critical magnetic field., as the superconducting contact metal, along with high mobility suspended graphene samples, we hope to measure the behavior of graphene Josephson junctions in the quantum Hall regime. However, difficulties involved in the suspension and annealing processes of fabricating suspended graphene Josephson junctions have made it necessary for us to to develop a new fabrication process for making suspended Josephson devices. Over the course of this project, we have developed a fabrication process which uses a flip-chip bonder and graphene deposited on PMMA films to make suspended graphene samples. With these suspended flakes, we have produced niobium-graphene-niobiun Josephson junctions which exhibit multiple Andreev reflection at temperatures of 4 K. and a Dirac peak near -0.4 V, all without any annealing of the graphene. We have also developed an annealing and lithography process which can clean graphene and preserve its cleaness during the rest of the fabrication process. This annealing process has yielded suspended graphene samples with mobility upwards of 200, 000 cm 2 V-i s-1 comparable with high mobility flakes presented in literature. / by Haofei Wei. / S.B.

Thesis: S.B., Massachusetts Institute of Technology, Department of Physics, 2003. / Cataloged from PDF version of thesis. / Includes bibliographical references (pages 32-33). / Asteroids are thought to be the source of all meteorites found on Earth. Numerous spectroscopic studies have been performed to try and link certain types of meteorites with certain classes of asteroids in space. However, these spectroscopic studies of meteorites and asteroids have often shown a discrepancy between the meteorite and asteroid spectra, with the asteroid spectra showing a higher red slope and less prominent absorption bands. This effect has been seen especially in the spectra of asteroids located in the main belt. Scientists now believe that space weathering processes, such as solar wind ion implantation and bombardment by micrometeorites, can affect the upper few millimeters of an asteroid's surface to produce the higher red slope and reduced absorption bands seen in spectra. However, asteroids in the near- Earth region, which are generally smaller than those found in the main belt, have not shown signs of space weathering as much as asteroids in the main belt. The purpose of this study was to investigate factors that might influence the appearance of near-Earth asteroid spectra, in particular the conditions at the time of observation. The two main observational conditions examined were the apparent magnitude of the object, or V-magnitude, and the angle between the Earth, object, and Sun, commonly called the Phase Angle. Running-box average plots and least-squares analysis was performed on a data set of 332 near-Earth asteroids to determine if any links could be made between the spectral characteristics and observational parameters. The most interesting finding of this study was a correlation in the SQ-complexes between the second spectral component, PC2', which indicates the presence or absence of an absorption band at 1 [mu]m, and the Phase Angle for the SQ-complex asteroids, suggesting that the observation angle affects the spectrum of an asteroid. One possible explanation may lie in the fact that the particle size of the asteroid surface must be much larger than the wavelength of the light to create the multiple scattering needed to reflect light in the direction of the Earth. / by Nancy P. Hsia. / S.B.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2010. / Cataloged from PDF version of thesis. / Includes bibliographical references (p. 151-156). / The study and prediction of velocities in the pedestal region of Alcator C-Mod are important aspects of understanding plasma confinement and transport. In this study, we examine the simplified neoclassical predictions for impurity flows using equations developed for plasmas with background ions in the Pfirsch-Schliter (PS, high collisionality) and banana (low collisionality) regimes. Measured B5+ flow profiles are derived from the charge-exchange spectroscopy diagnostic on Alcator C-Mod and are compared with calculated profiles for the region just inside the last closed flux surface. For the steep gradient region, reasonable agreement is found between the predictions from the PS regime formalism and the measured poloidal velocities regardless of the collisionality of the plasma. The agreement between the neoclassical predictions using the banana regime formalism and measured velocities is poorer. Additionally, comparisons of measured velocities from the low- and high-field sides of the plasma lead us to infer the strong possiblity of a poloidal asymmetry in the impurity density. This asymmetry can be a factor of 2-3 for the region of the steepest gradients, with the density at the high-field side being larger. / by Kenneth David Marr. / Ph.D.

Thesis (Ph.D.) Massachusetts Institute of Technology. Dept. of Physics, 1957. / Vita. Appendix contains numerous pamphlets. / Bibliography: leaves 115-117. / by Sol Aisenberg. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 1994. / Includes bibliographical references (p. 147-156). / by Paul Phong Nguyen. / Ph.D.

Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Physics, 2012. / Cataloged from PDF version of thesis. In title on title page, "the square root of sigma" appears as the mathematical symbol. / Includes bibliographical references (p. 109-112). / One of the primary goals of the spin physics program at the STAR experiment is to constrain the polarized gluon distribution function, [delta]g(X,Q²), by measuring the double longitudinal spin asymmetry, ALL, of various final-state channels. Neutral pions provide a potentially powerful final state because they are copiously produced in p+p collisions and have few backgrounds. In 2009, STAR took 14 pb-¹ of integrated luminosity of 200 GeV p+p collisions, with average beam longitudinal polarization of 59%. Neutral pions produced in these collisions can be identified using STAR's large-acceptance electromagnetic calorimeter, with help from tracking from the STAR Time Projection Chamber. This work presents a measurement of the inclusive neutral pion ALL from this data, based on a new [pi]⁰ reconstruction algorithm. A comparison to theoretical predictions and other experimental results suggests that the current best-fit value of AG, the gluon contribution to the proton spin, is too small and that [delta]G is actually comparable in magnitude to the quark contribution to the proton spin [delta][sigma]. / by William Leight. / Ph.D.