In the present thesis we have investigated the lattice dynamics of diamond on the basis of the Cochran version of the dipole approximation model. Results have been presented for the dispersion curves, vibration spectra and Debye temperatures of diamond. We have also obtained the vibration spectra and Debye temperatures of germanium.

The contents of the present thesis can be described as follows. In chapter II the work of Hone (H60) is extended and the results are combined with those of Bailyn (B60). A unified approach is given to the derivation of the "proton-electron" dielectric function, with simplifications achieved by the removal of certain unnecessary transformations. A discussion of electron-electron screening shows why many of the results derived from Bailyn's and Hone's work are similar. In chapter III new derivations are given for the exchange and correlation terms obtained by several authors, namely Toya (T58), Hubbard (H57), Geldart-Vosko (G65), Kleinman (K67), and Takahashi (T68). We then show that electron-electron screening can be described in a more accurate way, and using a factorization procedure (introduced in chapter II), new expressions for the exhange and correlation term are obtained. In chapter IV we present the lattice dynamics of sodium, potassium and rubidium. Cochran's (C63) method of obtaining empirical effective potentials from the dispersion curves is discussed to obtain some insight into the problem. Then the method of Cowley et al (C66) is applied; a choice of the dielectric function is made, the pseudopotentials are determined and compared to those obtained by least squares fitting of different models. Finally, the dispersion curves are calculated and the interatomic potentials are also obtained.

A dilatometer of exceptionally high sensitivity has been developed and used to measure the thermal expansion of polycrystalline samples of copper, silver and gold and of a single crystal of copper in the range 4.2 to 15°K. The results obtained for copper were in excellent agreement with the work of other researchers and the error estimates were sufficiently small to show that the theoretical calculations of Collins are not supported by measurements on a polycrystalline specimen of copper. Below 15°K the data points were well represented by the equation: 1010a=1.54+/-0.04 T+0.275+/-0.0027T 3 The results obtained for a single crystal of copper were significantly different from those obtained for a polycrystalline sample yet they are also in disagreement with the theoretical value. Below 15°K the data fitted the equation: 1010a=3.13+/-0.05 T+0.255+/-0.003T 3 Values of Yo (the low temperature limiting value of the Gruneisen parameter) for silver and gold were measured to be 2.04 +/- 0.06 and 2.91 +/- 0.02 respectively. The agreement with the theoretical values 2.22 and 2.92 is quite good. Below 6°K the thermal expansion of silver and gold was found to be anomalous as it was no longer proportional to the specific heat of these metals. In order to obtain high accuracy in the values of thermal expansion it was necessary to measure temperature to about 0.01°K. For this purpose a method was developed to obtain an interpolation of the resistance versus temperature function in the range 4.2 to 10°K. This capability permitted a theoretical study of the electrical resistivity of pure platinum which indicated that d-band electrons contribute significantly to the conductivity at low temperatures. In the hope of obtaining better measurements of temperature indium resistance thermometers were designed and constructed. Their reproducibilities were measured and were found to exceed previously reported values for indium resistance thermometers.

Abstract not available.

Abstract not available.

Apparatus has been constructed to measure the g-factor of free electrons by means of a "transverse Stern-Gerlach experiment". The g-factor has not yet been measured, but preliminary experiments have been performed. Some of the theoretical aspects of the experiment are discussed, and an order of magnitude for the effect calculated. Construction and operation of the apparatus is described, and suggestions for improvements given. Suggestions for a future experiment are given. / Science, Faculty of / Physics and Astronomy, Department of / Graduate

Indiana University-Purdue University Indianapolis (IUPUI) / Presented in this thesis is the construction of an apparatus to produce optically trapped lithium-6 atoms in the two lowest hyperfine states, the observation of cooling the trapped atoms by parametric excitation, and a study on the searching for itinerant ferromagnetism in a two-dimensional Fermi gas. In the parametric cooling experiment, a technique is developed to cool a cold atomic Fermi gas by parametrically driving atomic motions in a crossed-beam optical dipole trap. This method employs the anharmonicity of the optical dipole trap, in which the hotter atoms at the edge of the trap feel the anharmonic components of the trapping potential, while the colder atoms in the center of the trap feel the harmonic one. By modulating the trap depth with frequencies that are resonant with the anharmonic components, hotter atoms are selectively excited out of the trap while keeping the colder atoms in the trap, generating a cooling effect. An analytical study of itinerant ferromagnetism in a two-dimensional atomic Fermi gas is presented, based on the past experiments done with three-dimensional Fermi gases. Here, the formation of repulsive polarons in a strongly-interacting Fermi gas is used as an initial condition. Then the observation of itinerant ferromagnetism is realized by detection of ferromagnetic domains in the two-dimensional gas. Additionally, an experiment and simulation is performed on the effect of velocity-changing collisions on the absolute absorption of lithium-6 vapor in an argon buffer gas. The dependence of probe beam absorption is observed by variation of beam intensity and spatial evolution. The simulation of an effective three-level energy model with velocity-changing collisions determines a collision rate that agrees with transmission data collected.

No description available.

No description available.

No description available.