The fractional quantum hall effect under hydrostatic pressure

We report on experiments performed on a high quality, high carrier concentration heterostructure at a range of hydrostatic pressures. At a pressure of 1 bar a clear _xx minimum and Hall plateau were observed associated with a fractional state while no such structure was observed for the fractional state. At increasing pressure however structure in the resistivity components _xx and _xy for the state became increasingly pronounced. As the disorder in the sample and the measured activation energy for the state remained relatively unchanged with increasing pressure we speculate that the enhancement of the state with increasing pressure is due to an increase in the energy gap for this state.