Date of Award
Doctor of Philosophy
Physics and Astronomy
C. M. Soukoulis
The effects of the magnetic flux on the properties of disordered normal metal rings and bond or site diluted two-dimensional superconducting networks are investigated theoretically, with an emphasis on the quantum coherence of the electrons and the localization nature in the disordered systems. The conductance of disordered metal rings in magnetic field is obtained via the Landauer's formula through calculations of the localization length L[subscript] c. The important role of the ensemble averaging and the self-averaging to obtain the half-flux-quantum h/2e conductance oscillation is demonstrated unambiguously in both rings of a strictly one-dimensional geometry and rings with a finite width. The amplitude of the localization length oscillation is found to follow a universal relation for all the numerical data: [delta](L[subscript] c/L) = [alpha](L[subscript] c/L)[superscript]2. L is the radius of the ring. The expected universal conductance fluctuations are observed for L[subscript] c/L ~ 1. For L[subscript] c > L, much larger oscillation amplitudes are obtained. In the case of two-dimensional site or bond percolation superconducting networks, the nature of the eigenstates and the effects on the superconducting-to-normal phase boundary is examined by finite-size transfer matrix calculations within the mean-field Ginzburg-Landau theory of second order phase transitions. The fine structures of the T[subscript] c-H phase boundary are found to be washed out immediately when a small fraction of sites or bonds is removed. A rich structure for the mobility edge is obtained. The existence of two different phase boundaries, one for the first eigenstate and the other for the first mobility edge, may have important experimental consequences. ftn*DOE Report IS-T-1388. This work was performed under contract No. W-7405-Eng-82 with the U.S. Department of Energy.
Digital Repository @ Iowa State University, http://lib.dr.iastate.edu/
Li, Qiming, "Flux quantization effects in disordered normal metal rings and superconducting networks " (1989). Retrospective Theses and Dissertations. 9214.