| We have constructed a specialized experimental setup with integrated magnetic field independent thermometry, which has enabled us to cool the charge carriers in two dimensional electron gases down to 5 mK, and reliably measure the temperature. Using this setup, we have conducted studies of nu=5/2 fractional quantum Hall state(FQHS) in so far unexplored regions of the parameter space. Using a sample with a tunable density, we observe, for the first time, an evidence of a transition at nu=5/2 filling factor. This transition takes place at the lowest density at which nu=5/2 state had been measured to date, around 6x1010cm-2. Using a different set of samples, we also demonstrate a consistent way to account for the disorder contribution to the energy gap of nu=5/2 FQHS for several samples of vastly different densities. This lets us quantify, for the first time, the dependence of the experimentally measured intrinsic gap at nu=5/2 on Landau level mixing alone. Finally, we have conducted an ultra-low temperature study of the fractional quantum Hall states in the 1/3 |
