Upshift of the fractional quantum Hall plateaux: evidence for repulsive scattering for composite fermions

It is now established that if there are an equal number of positively and negatively charged impurities, the quantum Hall plateaux in ρxy(B) are expected to be centred about the classical value ρxy=B/(en) where n is the 2D carrier density. It has also been shown that when repulsive or attractive scattering centres are deliberately introduced close to a two-dimensional electron gas (2DEG), the centres of the quantum Hall plateaux are shifted to higher or lower magnetic field, respectively. In this paper, we present magneto transport measurements on a high-quality GaAs electron system. We extend this concept to the composite fermions where each electron is bound to two magnetic flux quanta. We provide compelling evidence that the dominant scattering for the composite fermions is different from that for electrons. This is supported by studying the upshift of the ν=1 quantum Hall plateau within the composite fermion picture.