Ground States of Interacting Electrons in the Extreme Quantum Limit

A review is given of selected collaborative experiments that we have carried out at Oxford, Saclay, Leuven, Grenoble and most recently Sydney, centred on the integer and fractional quantum Hall effects and the search for the electron solid in GaAs. The electronic ground state configurations is samples of the highest purity that have been fundamental to this programme, prepared by Philips Research Laboratories, UK, have been probed by a variety of novel techniques under extreme experimental conditions.