Some of the material in is restricted to members of the community. By logging in, you may be able to gain additional access to certain collections or items. If you have questions about access or logging in, please use the form on the Contact Page.
The purpose of this dissertation is to study different properties of the transition metal oxides, especially the high-Tc superconductors. Applying Monte Carlo methods to a Spin- Fermion model, the behavior of the band structure, Fermi surface, pairing correlations, and optical conductivity are studied. The numerical simulations are done at different temperatures, and densities relevant for the cuprates Previous Monte Carlo simulations of this model have shown the existence of charge stripes separated by anti ferromagnetic domains upon doping. These results are consistent with neutron scattering experiments. At half ling the ground state of the Spin-Fermion model is an insulator. The doped holes contribute to the formation of midgap bands by modifying the valence and the conduction band. The ground state appears to change from an insulator to a conductor. In the metallic regime the lower midgap and conduction bands overlap each other giving rise to a pseudogap in the density of states at the chemical potential. This agrees with the results from ARPES experiments. Both midgap and valence bands determine the Fermi surface. The D-wave pairing correlations, for all values of parameters, are stronger than S-wave. The D-wave pairing correlations are the strongest in the direction perpendicular to the dynamic stripes which appear in the ground state at some dopings. An optimal doping, where correlations are maximized, is observed close to 25% with an estimated critical temperature Tc = 100 200K in qualitative agreement with high-Tc cuprates phenomenology. The optical conductivity and Drude weight are studied as a function of electronic density and temperature. As temperature is reduced, spectral weight is transferred from high to low frequencies in agreement with the behavior observed experimentally. Varying the hole density, the Drude weight has a maximum at the optimal doping for the model are stronger. The inverse of the Drude weight, which is roughly proportional to resistivity, decreases linearly with temperature at the optimal doping, and it is abruptly reduced when robust pairing correlations develop upon further reducing the temperature. The general form of the optical conductivity is in good agreement with the experimental results for the cuprates.
A Dissertation Submitted to the Department of Physics in Partial FulﬁLlment of the Requirements for the Degree of Doctor of Philosophy.
Includes bibliographical references.
Adriana Moreo, Professor Directing Thesis; Sanford A. Safron, Outside Committee Member; Nicholas E. Bonesteel, Committee Member; Jorge Piekarewicz, Committee Member; Jianming Cao, Committee Member.
Florida State University
Use and Reproduction
This Item is protected by copyright and/or related rights. You are free to use this Item in any way that is permitted by the copyright and related rights legislation that applies to your use. For other uses you need to obtain permission from the rights-holder(s). The copyright in theses and dissertations completed at Florida State University is held by the students who author them.