Investigation of the electron-phonon interaction in the fractional quantum Hall regime using the thermoelectric effect

In the fractional quantum Hall regime (filling factor ν<1) the measured longitudinal and transverse components of the thermopower of the two-dimensional electron gas in GaAs-${\mathrm{Ga}}_{1\mathrm{-}\mathit{x}}$${\mathrm{Al}}_{\mathit{x}}$As heterojunctions behave qualitatively differently from those in the integer quantum Hall regime and also quite differently from the tensor components of the resistivity. They are both found to be almost field independent, making a jump of approximately a factor of 2 at ν=1/3. Since the thermopower is experimentally shown to be caused by phonon drag, this result implies a different electron-phonon coupling to the quasiparticle states below and above 1/3.