Experimental evidence for composite particles in the fractional quantum Hall effect

We have measured the temperature dependence of the transport coefficient ρ_xa at the lowest Landau level fractional quantum Hall effect filling factors v = ρ/(2p ± 1), up to ρ = 5, in a high-quality two-dimensional electron system. Our data establish that the gap energies separating the excitations from their quantum liquid ground states are linear with ΔB, the magnetic field deviation from exact half-filling. We interpret this linearity as evidence for Landau level quantization of composite particles and deduce the effective mass and the scattering times of the particles.