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Title: Frictional drag of two-dimensional electron gases
Author: Hill, N. P. R.
Awarding Body: University of Cambridge
Current Institution: University of Cambridge
Date of Award: 1998
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In this thesis measurements are presented of the frictional drag between two closely spaced but electrically isolated two dimensional electron gases, where the momentum transfer from a current in one layer is measured as a voltage in the adjacent layer. The drag measurement has been applied to this bilayer system under a number of different conditions. Firstly, at zero magnetic field and at temperatures comparable to the Fermi temperature, a new interlayer coupling mechanism is measured. The experimental traces are compared to a recent theory of the plasmon enhancement of the interlayer Coulomb coupling, which is shown to account for the observed behaviour. The drag is used to probe the bilayer plasmon modes, and it is shown that calculations in the random phase approximation provide an over estimate of the plasmon energies, which are reduced by many-body correlations. The fit to experiment is improved for calculations where the intra-layer exchange interaction is included in the Hubbard approximation. Next, the drag is measured in the presence of a magnetic field at temperatures sufficient to smear the Landau level structure. It is shown that the discrete energy spectrum of the electronic states leads to an enhancement of low energy scattering, which favours single particle Coulomb scattering as the dominant interlayer coupling. When the temperature is lowered into the QH regime, it is shown that the drag is more sensitive to the spin-splitting of the Landau levels than single layer transport measurements. It is also shown that the localised states in the Landau level tails, should be included in the theoretical models. A novel electron-hole symmetry applies to the interlayer scattering in this regime, and a scattering mechanism is suggested involving interedge scattering within each layer via localised states.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available