FQHE states of high mobility n-Si/Si_1-xGe_x heterostructures in pulsed magnetic fields

Low temperature (mK) magneto-transport measurements of high quality n-type modulation-doped Si/Si0.7Ge0.3 heterostructures have been extended to high magnetic fields (50T) and low temperatures (40mK). For the high mobility electrons confined to 2D in the biaxially tensile strained Si layer, a two-valley system, signatures of the fractional quantum Hall effect (FQHE) in the Landau level filling factor region ν<1 (one valley occupied, lowest spin state) usually observed in GaAs are replicated out to ν= 2 5 at B ∼ 48T. For 1<ν<2 however, (both valleys occupied, lowest spin state), prominent FQHE states such as ν= 5 3 are absent, similar to the case in double layer GaAs systems. Tilted field experiments demonstrate that the valley splitting depends only on the normal field component. © 1995.