FRACTIONAL QUANTUM HALL EFFECT MEASURED IN A SPIN DEGENERATE ELECTRON GAS

The influence of spin on the Fractional Quantum Hall Effect is investigated in GaAs-GaAlAs heterojunctions in a filling factor region where both spin states of the lowest Landau level are occupied. When the single particle spin splitting is reduced by hydrostatic pressure features at even numerator fractions are enhanced while those with odd numerators are diminished. This is due to the existence of spin- and Landau gaps in the composite Fermion energy spectrum. In this paper the influence of spin splitting on the Fractional Quantum Hall Effect (FQHE) is studied experimentally by reducing the energy difference between electron states of spin up and spin down with hydrostatic pressure. 1 The results are interpreted in the composite Fermion (CF) framework. Usually only one spin state is considered, i.e. the electrons are treated as spinless particles or in the limit of infinite spin splitting. Then the FQHE can be interpreted as an integer QHE of spinless CFs and all the features seen at high magnetic fields for filling factors ν<1 can be explained by forming CF Landau levels (LL) in an effective field centred on ν=1/2. 2 However, for 2>ν>1 and at low fields both spin states must be considered. By using hydrostatic pressure to tune the Landé g-factor we can investigate th