Interaction effects and disorder in two-dimensional electron systems

This thesis reports an experimental study of transport on a mesoscopic lengthscale in the localised regime of two-dimensional electron systems (2DES) with varying disorder. Devices with dimensions of a few microns were fabricated from modulation doped GaAs/ AlGaAs heterostructures, where the strength of disorder was tuned by changing the width of the undoped spacer layer separating the 2DES from the charged dopants, which are the main source of disorder in these systems. The main motivation of the experiments was to study the interplay between electron-electron interactions and short-range disorder at low electron densities, while avoiding the impact of long-range charge inhomogeneities that are usually present in this regime. Indeed, several new observations have been achieved with this approach: Chapter 5 reports an universal behaviour of hopping magnetoresistance, with evidence of the average hopping distance being equal to the average electronelectron separation, and a quantisation of the hopping prefactor in units of the quantum of resistance h/e2. Chapter 6 discusses the temperature dependence of resistance. The main result is an apparent temperature driven metal-to-insulator transition with a crossover from activated transport at high temperatures to metallic transport at low temperatures. This observation persists to resistivities of several hundred times the quantum of resistance. In chapter 7 a new kind of resistance oscillations is reported, which appear as a function of electron density when a strong perpendicular magnetic field is applied. A strongly amplified pick-up of the Shubnikov-de Haas oscillation and a modification of t he quantum Hall effect are reported in chapter 8. Furthermore, a new technique for measuring the electron density in mesoscopic 2DES is presented in chapter 4.

Name dc:type.qualificationname

Doctor of Philosophy (PhD)

Level dc:type.qualificationlevel

Doctoral

Grantor dc:publisher.institution

University of Cambridge

Year dc:date.issued

2008

Author dc:creator

• Baenninger, Matthias

Licence

• https://apollo8-f-pro.lib.cam.ac.uk/bitstreams/2e604e3b-28b4-42fd-aa65-1d409d4811de/download
• https://www.rioxx.net/licenses/all-rights-reserved/

Language dc:language

eng

DOI dc:identifier.doi

https://doi.org/10.17863/CAM.27508

OAI identifier oai:identifier

oai:www.repository.cam.ac.uk:1810/280142