Fractional quantum Hall effect in SiGe/Si/SiGe quantum wells in weak quantizing magnetic fields

We have experimentally studied the fractional quantum Hall effect in SiGe/Si/SiGe quantum wells in relatively weak magnetic fields, where the Coulomb interaction between electrons exceeds the cyclotron splitting by a factor of a few XX. Minima of the longitudinal resistance have been observed corresponding to the quantum Hall effect of composite fermions with quantum numbers $p=1, 2, 3$, and $4$. Minima with $p=3$ disappear in magnetic fields below $7$ T, which may be a consequence of the intersection or even merging of the quantum levels of the composite fermions with different orientations of the pseudo-spin, i.e., those belonging to different valleys. We have also observed minima of the longitudinal resistance at filling factors $\nu = 4/5$ and $4/11$, which may be due to the formation of the second generation of the composite fermions.