Fractional Quantum Hall Effect of p-Type GaAs-(GaAl)As Heterostructures in the Millikelvin Range

The magnetoresistance components pxxand pxy of modulation doped p-type GaAs-(GaAl )As heterojuncti ons were investigated between 50 mK and 4.2 K in magnetic fields B up to 12.5 T and in the temperature range of 400mK to 4.2K in fields up to 21 T. The high quality samples had hole mobilities up to 2.2×105 cm2/Vs and a carrier concentration around 2.3−2.5×1011/cm2 at the lowest temperature employed. Pronounced Shubnikov-de Haas oscillations and well-developed Hall plateaus were observed, especially at temperatures below 300 mK. Both the integral and the fractional quantum Hall-effect showed up with well-resolved steps in pxy at 50 mK. Plateaus with fractions with odd and even denominators were seen.