Valley Degenerate 2D Electrons in the Lowest Landau Level
  We report low temperature magnetotransport measurements on a high mobility (\mu=325,000 cm^2/V sec) 2D electron system on a H-terminated Si(111) surface. While low magnetic field data indicate a six-fold valley degenerate system, we observe the integral quantum Hall effect at all filling factors \nu<=6 and find that \nu=2 develops in an unusually narrow temperature range. An extended, exclusively even numerator, fractional quantum Hall hierarchy occurs surrounding \nu=3/2, consistent with two-fold valley-degenerate composite fermions (CFs). We determine activation energies and estimate the CF mass. 
Tomasz M. Kott, Binhui Hu, S. H. Brown, B. E. Kane
cond-mat.mes-hall cond-mat.str-el