Fractional quantum Hall effect in a two-dimensional hole system

We have studied the fractional quantization of the Hall resistance at 0.51 K in two-dimensional hole systems formed at p+:Ga1-xAlxAs-GaAs interfaces with mobilities as high as 8.0 × 104 cm2/Vs at 4 K. In addition to the Hall quantization for a fractional filling factor =23, we report for the first time the observation of an almost fully developed Hall plateau at =35 and the existence of weak but distinct structure in the magnetoresistance for =37 and 65. Similarly, magnetoresistance minima occurred at =53, 43, 23, 35, and 25. In contrast with two-dimensional electron systems, conspicuously absent was any magnetoresistance feature in the vicinity of =45.