SPECTROSCOPY OF PHONON EMISSION IN THE QUANTUM HALL-EFFECT REGIME

Phonon emission from two-dimensional electron gases in the quantum Hal l effect (QHE) state of a Si MOSFET was measured using the phonon-indu ced conductivity of the substrate. The inherent phonon energy detectio n threshold of this system was used to analyze the frequency spectra o f the phonons in strong magnetic fields. It was found that phonons wit h cyclotron energy are emitted in the QHE state. The emission takes pl ace in the corners of the Hall bar sample where the current enters and exits. This observation probably indicates that, in the QHE state, th e temperature of the electrons in the corners rises sufficiently to al low inter-landau-level transitions.