Enhancement of the 4/3 fractional quantum Hall state with hydrostatic pressure

The authors report on experiments performed on the fractional quantum Hall effect under hydrostatic pressure. At roughly comparable carrier concentrations the application of pressure results in a significant enhancement of the 4/3 state in the three Al x Ga 1-x As/GaAs samples studied. As the variation in disorder with pressure is different in the three samples the authors are able to establish that the 4/3 activation energy has a pressure dependence in addition to that due to the change with disorder. They propose that the observed enhancement of activation energy is due to a reduction in the value of the modulus of the Lande g-factor in the GaAs with increasing hydrostatic pressure and to the 4/3 state being spin unpolarized.