Resistance scaling for Composite Fermions in the presence of a density   gradient
  The magnetoresistance, Rxx, at even-denominator fractional fillings, of an ultra high quality two-dimensional electron system at T ~ 35 mK is observed to be strictly linear in magnetic field, B. While at 35mK Rxx is dominated by the integer and fractional quantum Hall states, at T~1.2K an almost perfect linear relationship between Rxx vs B emerges over the whole magnetic field range except for spikes at the integer quantum Hall states. This linear Rxx cannot be understood within the Composite Fermion model, but can be explained through the existence of a density gradient in our sample. 
W. Pan, H.L. Stormer, D.C. Tsui, L.N. Pfeiffer, K.W. Baldwin, K.W.   West