LOCALIZATION AND ELECTRON-ELECTRON INTERACTION EFFECTS IN THIN GOLD-PALLADIUM FILMS AND WIRES

JUHN-JONG LIN, Purdue University

Abstract

We have conducted extensive measurements of the low temperature magnetoresistance of thin gold-palladium (Au-Pd) films and very small diameter Au-Pd wires. These results have been used to determine the importance of localization and electron-electron interaction effects in these systems. 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. From the measurements as a function of magnetic field, we have determined the inelastic scattering time, (tau)(,i), the spin-spin scattering time,(tau)(,s), and have placed an upper limit on the spin-orbit scattering time, (tau)(,so). We found that (tau)(,s) is essentially the same for the films and wires, as expected since this is predicted to be a material (i.e., bulk) property which should be independent of dimensionality. The upper limit on (tau)(,so) in one and two dimensions are also consistent. In contrast, (tau)(,i) depends on the dimensionality of the sample, and has distinctly different temperature dependence in the two cases. In the films it appears to be due to electron-electron scattering in the presence of disorder in the two-dimensional limit. In the wires it is due to the one-dimensional version of this scattering mechanism. This appears to be the first experimental observation of one-dimensional electron-electron scattering in "metal" wires. We have also extended measurements of this kind to study in more detail the variation of (tau)(,i) and (tau)(,s) as the thickness, d, the resistivity, (rho)(,e), and the method of preparation of the Au-Pd are varied. We have found that the magnitude of (tau)(,i) for high resistivity (i.e., sputtered) films is in good agreement with the theory, while the magnitude of (tau)(,i) for low resistivity (i.e., thermal evaporated) films is not. In addition, we have found that the spin-spin scattering time, (tau)(,s), varies as d and (rho)(,e) are changed. The observed variation of (tau)(,s) does not appear to be consistent with current ideas concerning the source of this scattering.

Degree

Ph.D.

Subject Area

Condensation

COinS