LOCALIZATION, ELECTRON-ELECTRON INTERACTION, AND UNIVERSAL CONDUCTANCE FLUCTUATION PHENOMENA IN THIN BISMUTH FILMS AND WIRES
Abstract
We have performed extensive resistance and magnetoresistance measurements on Bi films and wires in order to test the predicted effects of localization, electron-electron interactions, and universal conductance fluctuations in these systems. The overall behavior found in two dimensions agrees fairly well with previous results for Bi, and with the theory. The magnetoresistance in the small magnetic fields employed in this work (<10 >kG) appears to be due predominantly to localization. Both localization and interactions contribute to the variation of the resistance with temperature in zero field, with interactions generally being dominant. The inelastic scattering in the films is found to be three dimensional electron-electron scattering in the presence of disorder, and agrees well with the theory of this process, except that the length scale determining the dimensionality appears to be shorter than predicted by theory. The results in one dimension are also found to agree well with the theory, and the magnetoresistance in small magnetic fields is due predominantly to localization. In zero magnetic field, interactions play a dominant role in the smallest wires, but in larger wires with a slightly different geometry we find that localization can be dominant. This is the first instance where localization in the presence of strong spin-orbit scattering (anti-localization) has been observed to dominate over electron-electron interaction effects. In the larger wires, the inelastic scattering is found to be due to electron-electron scattering in the presence of disorder, approaching the three dimensional limit seen in the films. In the smallest wires, the inelastic scattering has a much weaker temperature dependence which lies between that predicted for one and two dimensional electron-electron scattering. Again, as in the films, the length scale determining the dimensionality of the wires does not seem to be consistent with the theory. We have observed resistance fluctuations in thin Bi wires and films. The magnitude and temperature dependence of the fluctuations are in reasonable agreement with the theory of universal conductance fluctuations in disordered conductors. This is the first time that fluctuations have been seen as a function of time in metal wires or in any two dimensional structure.
Degree
Ph.D.
Subject Area
Condensation
Off-Campus Purdue Users:
To access this dissertation, please log in to our
proxy server.