Even-Denominator Filling Factors in the Thermoelectric Power of a Two-Dimensional Electron Gas

We have investigated the interaction of phonons with a two-dimensional electron gas in the fractional quantum Hall regime with phonon drag thermoelectric power (TEP). The TEPs at filling factors with the same even denominator are found to be identical; at other even-denominator filling factors they differ only by a constant factor. Treating these states as composite fermions, the findings are explained by a zero magnetic field theory for phonon drag. A maximum observed in the TEP at $\nu =\frac{1}{2}$ is modeled by a weakly diverging effective mass of the composite fermions at this filling factor.