The Fractional Quantum Hall Effect in Semiconductor Heterostructures

Available from UMI in association with The British Library. Requires signed TDF. The fractional quantum Hall effect (FQHE) is observed in high quality two-dimensional electron systems at milli -Kelvin temperatures, in high magnetic fields. Plateaux develop in the Hall resistance, at quantised values given by R_{rm H} = ph/qe ^2; these plateaux are accompanied by minima in the longitudinal resistivity. The FQHE is a result of electron-electron correlation effects, which cause the electrons to form a incompressible fluid ground state; the elementary excitations of this ground state are quasiparticles, which carry the charge e/q. The initial theories of the FQHE were formulated upon the assumption that the electrons formed a fully spin polarised state. This is found not always to be true. The low field spin polarisations are determined for a number of FQHE states; these are found to agree with recent finite size calculations. The FQHE in the lowest Landau level is studied in high magnetic fields, where the ground states are all fully spin polarised, and the hierarchical model, which predicts the relative strengths of the FQHE states is found to be obeyed. The n = 1 Landau level is studied, and Hall plateaux are observed for the first time. However, there are features in the longitudinal resistivity in this Landau level which do not seem to be due to the FQHE. Cyclotron resonance is performed in a dilution refrigerator for the first time; the CR is brought into, and out of, coincidence with a strong FQHE state. No anomalous effect is seen in either the resonance position or linewidth. Microwave studies of the FQHE are performed, but no absorption corresponding to the FQHE energy gap is seen. Until now, the FQHE has been only observed in two 2-D system (Si-MOS structures and GaAs/GaAlAs heterojunctions). A quantised plateau at a fractional filling factor ( nu = 4over 3) is observed for the first time in a GaAs/GaAlAs quantum well.