Observation of composite-fermion thermopower at half-filled Landau levels

Measurements of the diagonal magnetothermopower (Sxx) of a high-quality two-dimensional hole system reveal that in the diffusion regime (T<100 mK), Sxx at filling factors =1/2 and 3/2 depends approximately linearly on temperature and has a much smaller magnitude than expected for noninteracting particles at half-filled Landau levels. We show that both the temperature dependence and the magnitude of Sxx at these two fillings can be explained remarkably well based on a recently proposed particle-flux composite-fermion picture.