Techn. Universiẗat, Diss., 2000--Darmstadt.

No description available.

No description available.

No description available.

A feedback technique is presented for the reduction of the Shoenberg magnetic interaction in metals. The method allows the spin splitting parameter g[sub c] for extremal orbits on the Fermi surface to be obtained from de Haas-van Alphen measurements, now essentially free from the oft-times severe distortions resulting from magnetic interaction. The feedback technique also offers several advantageous side effects, the most important one being a simple and reliable method for determining absolute amplitudes of de Haas-van Alphen oscillations. Explicit formulae are derived showing the dependence of several key observable quantities on the amount of magnetic feedback, and these formulae are found to be in good agreement with experiment. The technique is applied to the determination of g[sub c] for the [110] γ oscillations in Pb. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

A dissertation submitted to the Faculty of Science, University of the Witwatersrand, Johannesburg, in fulfilment of requirements for the degree of Master of Science. Johannesburg, 2015. / Recently there has been signi cant interest in new types of metals called non-Fermi liquids, which cannot be described by Landau Fermi liquid theory. Landau Fermi liquid theory is a theoretical model used to describe low energy interacting fermions or quasiparticles. There is a growing interest in constructing an e ective eld theory for these types of metals. One of the paradigms to understand these metals is by the use of Wilsonian renormalization group (RG) to study a theoretical toy model consisting of fermions coupled to a gapless order parameter eld. Here we will study fermions coupled to gapless bosons (order parameter) below the upper critical dimension (d = 3). We will treat both fermions and bosons on equal footing and construct an e ective eld theory which only integrates out high momentum modes. Then we compute the one-loop RG ows for the Yukawa coupling and four-Fermi interaction. We will discuss log2 and log3 subleties associated with the one loop RG ows for the four-Fermi interaction and how they can be circumvented.

In a thermally equilibrated system, electron behavior in a metal is described by the Fermi-Dirac equation. With ultrafast lasers, electrons can be excited into temporary distributions which are not described by the Fermi-Dirac equation and are therefore not at a well-defined temperature. These nonthermal distributions quickly equilibrate through two primary processes: electron-electron scattering and electron-phonon scattering. In most situations, these effects are unnoticeable, since they are completed within 5 ps. A probabilistic numerical model for electron-electron scattering is presented. The model is robust, scaleable, and requires only one parameter. The success of the model suggests future work on a similar electron-phonon scattering model, which would provide a complete description of the elctron distribution during thermalization. Once complete, this model can be tested by measuring the amount of second harmonic light generated by an ultrafast laser in a pump-probe experiment.

Thesis (Ph. D.)--Florida State University, 2003. / Advisor: Dr. Zachary Fisk, Florida State University, College of Art and Sciences, Dept. of Physics. Title and description from dissertation home page (viewed Mar. 2,2004). Includes bibliographical references.

Recent advances in using microscopes in ultracold atom experiment have allowed experimenters for the first time to directly observe and manipulate individual atoms in individual lattice sites. This technique enhances our capability to simulate strongly correlated systems such as Mott insulator and high temperature superconductivity. Currently, all ultracold atom experiments with high resolution imaging capability use bosonic atoms. In this thesis, I present our progress towards creating the fermionic version of the microscope experiment which is more suitable for simulating real condensed matter systems. Lithium is ideal due to the existence of both fermionic and bosonic isotopes, its light mass, which means faster experiment time scales that suppresses many sources of technical noise, and also due to the existence of a broad Feshbach resonance, which can be used to tune the inter-particle interaction strength over a wide range from attractive, non-interacting, and repulsive interactions. A high numerical aperture objective will be used to image and manipulate the atoms with single lattice site resolution. This setup should allow us to implement the Hubbard hamiltonian which could describe interesting quantum phases such as antiferromagnetism, d-wave superfluidity, and high temperature superconductivity. I will also discuss the feasibility of the Raman sideband cooling method for cooling the atoms during the imaging process. We have also developed a new electronic control system to control the sequence of the experiment. This electronic system is very scalable in order to keep up with the increasing complexity of atomic physics experiments. Furthermore, the system is also designed to be more precise in order to keep up with the faster time scale of lithium experiment. / Physics

We report here the results of a de Haas-van Alphen (dHvA) investigation of the coupled orbit system in magnesium. The data were taken for magnetic fields extending to 52 kG and temperatures down to 0.29° K. The experimental data are interpreted in the light of coupled orbit system theories of Pippard and of Falicov and Stachowiak; these are each reviewed in some detail. The data are found to disagree qualitatively with the predictions of Falicov and Stachowiak. Since this theory has been assumed, for more than a decade, to be equivalent to Pippard's theory, a detailed comparison of these was made. Full spectrum Fourier analysis of Pippard's band structure density of states shows that the two models disagree qualitatively and, therefore, that they are not equivalent. These experimental results, which do not appear to disagree with Pippard's theory, are interpreted to mean that it is fnally possible to obtain crystals of sufficient purity and perfection to make it necessary to use a band structure description of the delocalized electrons on the couple network. Evidence is presented for the existence of a new type of dHvA frequency corresponding to the ΓKM plane cross-section of the Brillouin zone. A proposed explanation for this dHvA frequency involves the field dependent modulation of the zero frequency component of the Fourier transform of the coupled orbit system density of states. Also included are discussions of crystal preparation and handling, cryogenic apparatus, analogue detection apparatus, digital data acquisition and processing hardware based on a microcomputer, and a new software system ideally suited to small computer research environments.