Anomalous robustness of the 5/2 fractional quantum Hall state near a   sharp phase boundary
  We report magneto-transport measurements in wide GaAs quantum wells with tunable density to probe the stability of the fractional quantum Hall effect at filling factor $\nu = $ 5/2 in the vicinity of the crossing between Landau levels (LLs) belonging to the different (symmetric and antisymmetric) electric subbands. When the Fermi energy ($E_F$) lies in the excited-state LL of the symmetric subband, the 5/2 quantum Hall state is surprisingly stable and gets even stronger near this crossing, and then suddenly disappears and turns into a metallic state once $E_F$ moves to the ground-state LL of the antisymmetric subband. The sharpness of this disappearance suggests a first-order transition. 
Yang Liu, D. Kamburov, M. Shayegan, L.N. Pfeiffer, K.W. West, K.W.   Baldwin
cond-mat.mes-hall cond-mat.str-el