BALLISTIC PHONON ABSORPTION IN THE FRACTIONAL AND NON-QUANTIZED HALL-EFFECTS

We have measured the direct absorption of ballistic phonons by a two-d imensional electron system (2DES) in the fractional quantum Hall regim e. We show experimentally that the electron-phonon interaction in our heterojunction sample is dominated by coupling to TA phonons. At odd i nteger denominator fractional filling factors a strong non-equilibrium heating of the 2DES is observed which can be attributed to excitation s across the magneto-roton gap. Away from fractional minima, in partic ular at a filling factor, v = 1/2, a much smaller temperature increase is found. (C) 1998 Elsevier Science B.V. All rights reserved.