We report the fabrication and characterization of a high-quality two-dimensional electron system in the X-point valley of an AlAs quantum well. The modulation doped structure has a density of n s =2.5×10 11 cm -2 and low-temperature mobility μ=3×10 4 cm 2 /V s. Cyclotron resonance data reveal an effective mass m c =0.46m 0 , indicating that the X-point conduction valleys with heavy in-plane mass are occupied. In the magnetotransport data, we observe quantum Hall states at consecutive integral Landau-level fillings (ν), implying that the degeneracy of these valleys is lifted. Our data at high magnetic fields show well-developed fractional quantum Hall states at ν=1/3 and 2/3 with a gap of 1/3 Δ=1.3K for the ν=1/3 state at B≊30 T.
All Science Journal Classification (ASJC) codes
- Physics and Astronomy (miscellaneous)