COMPOSITE FERMIONS IN THE NEIGHBOURHOOD OF FILLING FACTOR 3/2

D.R. Leadley^1,2, P.J. Gee², R.J. Nicholas², J. Singleton², D.M. Maude³, J.C. Portal³, S. Udi⁴, J.J. Harris⁵ and C.T. Foxon⁶

1. Department of Physics, University of Warwick, Coventry CV4 7AL
2. Department of Physics, Clarendon Laboratory, Parks Road, Oxford, OX1 3PU
3. Laboratoire des Champs Magnetiques Intense, CNRS, F38042 Grenoble, Cedex 9, France
4. National Research Institute for Metals, Tsukuba Magnet Laboratories, 1-2-1 Sengen, Tsukuba, 305 Japan
5. Department of Electronic Enginering, University College, London
6. Department of Physics, Nottingham University, University Park, Nottingham

The Fractional Quantum Hall Effect (FQHE) is neatly described by a model of spinless Composite Fermions (CFs), allowing us to interpret it as an Integer QHE of the CFs. In this work we begin to test experimentally the consequences of including electron spin into the picture. We investigate the situation near \nu=3/2 where electrons of both spin states are present. We also compare CF energy level schemes arising from attaching flux tubes either to electrons or holes, and look at how these influence different FQHE minima.

The importance of spin splitting is studied by changing the relative size of this splitting in the experiments. It may be increased by either tilting the magnetic field or increasing the electron density and decreased by applying hydrostatic pressure. When the spin splitting is increased the features at \nu=4/3 and 8/5 decrease in strength relative to those at 5/3 and 7/5, and at higher tilt angles become stronger again, indicating a change in spin polarisation. At high pressures, where the g-factor approaches zero, even numerator fractions such as \nu=2/3, 4/3, 4/5 and 6/5 are enhanced while the odd numerator fractions are suppressed. This is consistent with removal of the spin degeneracy.

Presented at: Institute of Physics, Condensed Matter and Materials Physics Conference, Liverpool 1995