Abstract:

This thesis presents the results of a detailed experimental study of the Coulomb drag effect in dilute double layer two-dimensional hole systems, with rs ranging from roughly 10 to 20. The drag technique provides an extremely powerful probe of carrier interaction, as it directly measures the interlayer carrier-carrier scattering rate in a double layer system. We accompany these drag measurements with the corresponding single layer transport data. The resistivity of the individual layers exhibits an anomalous metallic temperature dependence and in-plane magnetoresistance, as is typically observed in dilute 2D systems near the metal-insulator transition.

At zero magnetic field, we find that the drag resistivity exhibits a two to three orders of magnitude enhancement over that expected from Boltzmann theory and the corresponding low density electron results. Furthermore, the temperature dependence of the drag exhibits significant deviations from the T2 dependence expected from Fermi liquid theory, which correlate with the anomalous metallic temperature dependence in the single layer resistivity. We show that these anomalous results are not consistent with previously studied drag mechanisms but rather arise from a novel mechanism related to the large rs value of the system.

We have also performed studies in the presence of an in-plane magnetic field, to investigate the effect of spin polarization on the drag in this regime. Strikingly, we find that both the drag and single layer resistivities exhibit the same qualitative dependence on B|| , with both showing similar features associated with spin polarization. Furthermore, we find that the temperature exponent of the drag exhibits an unusual dependence upon spin polarization. Near the metal-insulator transition.

the temperature dependence of the drag, given by T ? weakens significantly with the application of an in-plane magnetic field, with ? saturating at half its zero field value for B|| > B *, where B * is the polarization field.

Although the drag results presented in this thesis are highly anomalous, we find that they exhibit striking qualitative and quantitative similarities to the metal-insulator transition anomalies found in the single layer resistivity. We conclude by discussing both Fermi liquid and non-Fermi liquid based theoretical studies attempting to explain these results.