The two-flux composite fermion series of fractional quantum Hall states in strained (100) Si

Magnetotransport properties are studied in a high-mobility 2DES in the strained Si quantum well. We observe around v = 1/2 the two-flux composite fermion (CF2) series of the FQHE states at v = 2/3, 3/5, 4/7, and at v = 4/9, 2/5, 1/3. Of the CF series, the v = 3/5 state is weaker than the nearby 4/7 state and the 3/7 state is missing, resembling the observation that the v = 3 is weaker than the v = 4 state. Our data indicate that the CF model still applies for the multivalley Si/SiGe system when taking into account the two-fold valley degeneracy.